How do keywords work in paid search?

If you've been following along, you should by now know that there are these rather important things in paid search called keywords. They exist in ad groups (which in turn exist in campaigns), and they define what search terms you bid in.

Let's stop here for a second and make sure we're clear on the distinction between a keyword and a search term. A keyword is an entity that exists inside your account. A search term is something that a user types into a search engine. A keyword defines which search terms you bid on, but it's not identical to a search term.

With that in mind, how exactly does a keyword define which search terms you bid on?

Understanding match types

To understand the relationship between keywords and search terms, we first have to understand the different types of keywords, known as different match types.

How do exact match keywords work?

We've actually seen one match type already, exact match. This is the simplest type of keyword, and it (with some exceptions that we'll get to) denotes a one-to-one matching between keyword and search term. To put that less abstractly, a keyword of swimming costume that has an exact match type will only show ads on the search term swimming costume (italics to show that it's a search term). Simple.

We denote exact match keywords by wrapping them in square brackets. So, a keyword of [swimming costume] is basically an instruction to Google to show ads on the search term swimming costume.

How do close variants work?

I mentioned that there were some exceptions up above, and it's important that we cover them. While the preceding paragraphs would've been a perfectly good description of how exact match keywords worked back in 2017, Google have made some changes to their functioning since then. The main change they've made is to include what are called exact match close variants.

A close variant of an exact match keyword is a search term which is either:

There are a couple of other edge cases where close variant matching can kick in, which you can read up on here, but the above are definitely the ones most worth knowing about.

What does this mean for exact match?

You might have guessed it; the above means that exact match really isn't all that exact. For this reason, Google's moves to push close variants over the past few years have been controversial, and fuelled allegations that Google is simply trying to increase ad revenues by broadening the scope of exact keywords.

There is an alternative argument though, which states that close variant matching is actually beneficial for performance. No advertiser is going to be able to list every misspelling of their brand's key search terms for instance, and so a helping hand from Google isn't a totally bad thing.

Whatever your take on the issue is, remember that close variant matching exists (unless you want a shock when you go to look at what search terms you're appearing on).

With exact match covered, let's move onto the next keyword match type.

How do broad match keywords work?

Whereas exact match keywords create a one-to-one relationship between keyword and search term (close variants aside), broad match keywords create a one-to-many relationship between keyword and search term. We'll write broad match keywords with single quotes, like 'credit card'.

The keyword 'running shoes' is eligible to show ads on really any search term related to running shoes. It could be running shoes for men, best shoes to run a marathon in, or shoes for running fast. All of the close variant logic discussed above applies to broad match keywords (note how running changed to run in the middle example; the stemming was removed).

A broad match keyword like 'running shoes' differs from an exact match keyword like [running shoes] in that the former has a lot more flexibility in terms of terms it can bid on. One of my example search terms, best shoes to run a marathon in, wouldn't be picked up by [running shoes] but would be picked up by 'running shoes'.

Another crucial aspect of broad keywords which is exemplified by best shoes to run a marathon in is that ordering is unimportant. Even though 'running' comes before 'shoes' in the keyword 'running shoes', the keyword can still bid on search terms where the order is reversed. This likely isn't going to make a lot of difference if you're in the running shoe industry, where running shoes and shoes running have the same intent. An example of where it's far more important though is in travel, where an airline might want to bid on new york london but not on the reverse (london new york).

Do people actually use broad match keywords?

No, not really.

Because the matching on broad match keywords is so imprecise, you don't often see experienced paid search marketers using them. If you look at all the examples I gave above of search terms that could match against 'running shoes', you'll see a diverse range of search intents.

For example, consider the search terms credit card and apply credit card. People searching the former have weaker intent, and are likely researching credit cards. People searching the latter have likely already made up their mind to apply for a credit card, giving them a very different search intent.

Because one broad keyword can bring in such a diverse range of search intents, it's often better to replace the broad keyword with lots of different exact match keywords which can capture all the different search intents. If these exact match keywords are placed in separate ad groups (regardless of whether they're SKAG or STAG), you can then serve different ads on each keyword to best capture those users' search intent.

For example, lets say I have a product page of running shoes for men, and a blog article about shoes to run a marathon in. Instead of having one broad keyword that bids on all running-shoe-related terms, it'd make far more sense for me to have separate ad groups and keywords that focus on terms like running shoes for men and shoes to run a marathon in individually. Doing so is likely to give me better auction performance (due to better ad relevance, better CTRs, and better landing page experience), more traffic, and a higher conversion rate (from serving people relevant content). It's a no-brainer.

For this reason, broad keywords typically see very little use.

How do broad match modified (BMM) keywords work?

For those seeking something part way between broad and exact match keywords, look no further than BMM. BMM keywords are written the same as broad keywords, but with plus signs in front of each word; '+running +shoes' for example. This keyword will bid on any search term which contains both the terms 'running' and 'shoes', regardless of order.

BMM keywords aren't so loose that they match against anything vaguely related to running shoes, but not so strict that they only bid on one term in a specific order. Because of this, they're often used to pick up more long-tail search terms.

No advertiser can predict every which way a searcher will use running and shoes in a search term, so having a keyword like '+running +shoes' allows the advertiser to hoover up long-tail searches like running shoes that don't overheat without having to build out a near-infinitely long list of exact match keywords. Regular broad match keywords do this too, but they carry an additional risk of bidding on less relevant searches, as they don't require the keyword terms to appear in a user's search term.

How do advertisers use BMM keywords in practice?

A common approach is to use BMM in conjunction with exact keywords. The theory is that you should have exact keywords for all of your most important terms (head terms), and use BMM keywords to pick up lower-volume search terms related to your core exact keywords.

We'll cover exactly how to implement this later on, in the campaigns section. The only other thing worth knowing for now is that there are a variety of approaches one can take when deciding which exact keywords to build as BMM keywords. Personally I like to have complete parity between the two; one BMM keyword for every exact keyword. Not only does the one-to-one mapping satisfy a certain OCD, but it also means that I can pick up as much volume as possible.

The only exception that I'll make to my approach above is that I'll sometimes pause BMM keywords that are very short, especially those that are one word long. For example, I might bid on the exact keyword [running], but I'd never want to bid on the BMM keyword '+running'. The reason is that the latter could pick up search terms totally unrelated to the sport of running; who is running for president for example.

One point that's worth flagging now, even though we will cover it in more detail later on, is that things can get a bit messy when you're running BMM and exact keywords simultaneously. Because '+running +shoes' and [running shoes] can both bid on the search term running shoes, you have to do a bit of extra setup to ensure that they don't actually overlap, and that exact matches get left to the exact keyword. We'll come back to this in the campaigns section.

How do phrase match keywords work?

The last major keyword type in paid search is phrase match. We write phrase match keywords with double quotes; "running shoes" for example. A phrase match keyword will bid on all search terms that contain the phrase match keyword. So, our example keyword will bid on search terms like running shoes for sale, or buy running shoes, but never running road shoes or shoes for running.

Phrase match keywords aren't used as commonly as broad, BMM, or exact match keywords. The one advantage they have is in providing a middle ground between BMM and exact keywords. They do this by requiring that search terms be in a particular order (making phrase match more rigid than BMM) but also allowing for additional terms to prefix or suffix the phrase (making them less rigid than exact).

Who uses phrase match keywords?

The main use for phrase match keywords is in accounts that bid on terms where ordering is critical. If you're a brand that's selling package holidays from London to New York, a phrase match keyword like "london to new york" might make sense in your account.

You wouldn't want search terms like new york to london coming in (assuming you don't offer that package), so you can't use BMM or broad keywords. This is because both of these keyword types don't place any constraints on ordering. A keyword like +london +to +new +york would bid on searches like new york to london, a situation you want to avoid.

The best thing to do therefore is to use phrase match keywords in combination with exact match keyword. Your exact match keywords will be your main focus, because you know exactly what traffic is coming through them (close variants aside). Your phrase match keywords will help you keyword mine, safe in the knowledge that you'll only be bidding on terms that contain the phrase london to new york.

What is a phrase match modified (PMM) keyword?

There is one last type of keyword to cover, PMMs. PMMs are rarely seen in the wild, and you're unlikely to need them. That said, I did preface this guide by saying it's everything I know about search, so I'm obliged to include them.

A PMM keyword is essentially a mix between a BMM keyword and a phrase match keyword. When we looked at BMM keywords, we saw that they required a plus sign before each word (e.g. +running +shoes). One potential downside of this is it treats each word as an independent entity, and it doesn't respect ordering in the same way as a phrase or an exact keyword does. PMMs get round this by allowing you to broad match modify a phrase.

To see why this is interesting, let's imagine you're back running the package holiday brand. You can't bid on anything like +london +to +new +york, lest you show on searches trying to book a ticket to London. What you could do though is bid on a PMM keyword like The dots effectively act as spaces, and concatenate all the words into a phrase which the plus sign acts on. This keyword will bid on any search term that contains the phrase london to new york.

But wait, isn't this just phrase match? So far, yes! Where it gets interesting is in the fact that you can add additional parts to a PMM keyword. For example, our PMM keyword can be extended to something like +flight, which will bid on any search term that contains both london to new york and the word flight. You can't achieve this construction with a plain old phrase match keyword.

You don't just have to add BMMs either. You can add a broad keyword (e.g. holiday; which will bid on things like london to new york tour) or even another PMM (e.g. +flight.ticket, which will bid on things like london to new york buy flight ticket).

Don't get me wrong, you're not likely to use PMMs. I don't think I ever have. It's great to know they exist though, in case you ever find yourself in a situation where the ordering of your brand's search terms is critical to whether they're relevant or not.

Keywords: in summary

As you can see from the above, there are plenty of different types of keywords. While most accounts use just two or three (most commonly exact and BMM) it's crucial to understand all the different types in case you find yourself in a situation where you need to use a less common keyword type.

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