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LSI Keywords: What You Need to Know About Latent Semantic Indexing

LSI keywords are a commonly misunderstood concept in the SEO community. What is an LSI search engine? What is LSI in SEO? Learn more about what LSI is (and what it isn’t), then stick around for some best SEO practices for semantic keyword research.

Dec 21, 2021

4 m read

You might have heard that LSI keywords are the secret sauce that will boost your Google search rankings. You also might have heard that LSI-based SEO is the golden ticket because Google uses LSI technology to index web pages.

Ask a group of SEOs for a show of hands for who uses LSI keywords, and you’ll get a roomful of pockets.


Because there’s no such thing as LSI keywords.

twitter post from John Mueller saying there's no such thing as LSI keywords.

The LSI SEO myth was born in the 1980s, and for some reason, it persists to this day, constantly confusing site owners and marketers.

Let’s set the record straight.

What is LSI?

LSI stands for Latent Semantic Indexing, also known as Latent Semantic Analysis (LSA). LSI is a natural-language processor developed in the 1980s to address the issue of synonyms and polysemic words in search.  

English 101 Mini-Refresher

  • Synonyms are different words with similar meanings, such as fall and autumn.
  • Polysemic words sound and look the same but have different meanings, such as fall (off a chair) and fall (the season when leaves change colors). 

The creators of LSI technology defined the problem this way:

The basic problem may be simply summarized by stating that people want to access information based on meaning, but the words they select do not adequately express intended meaning.”

Patent for Computer information retrieval using latent semantic structure

Engineers developed LSI search engines to determine the relationships between words and phrases on a page. 

Isn’t history fun?

Fast forward to present-day search engines.

Does Google Use LSI?

Given how LSI solves for semantic search, it’s understandable that people would jump to the conclusion that Google’s using LSI tech to do the same thing. But it isn’t. Instead, it’s more likely that Google uses synonyms and polysemic words in its algorithm. 

How do we know?

First, LSI tech is really old — as in, before there was an internet, old. It wasn’t designed to work on the scale that Google does.

Second, Google’s algorithm can flex in a dynamically changing online landscape. Every day, millions of content pages are added, deleted, and changed. LSI can’t work in that environment. Every time there’s a change in stored files, it needs to re-index from scratch. Imagine the computing power it would take to do that on a global scale several times a day, every day.

What are LSI Keywords?

So why are we talking about something that doesn’t exist? Because everyone else is! When you hear people in the SEO community-at-large talking about LSI keywords, they’re talking about words and phrases that Google sees as semantically related to a topic.  

“LSI Keywords” = “Semantically-Related Keywords”

An entire subset of the SEO community on the internet is talking about LSI keywords when they should be discussing semantically-related keywords.

What Are Semantically-Related Keywords?

Semantic keywords are keywords that are conceptually related to your primary keyword. For instance, if you want to rank a page for “cold brew coffee,” Google looks on your page for related terms, such as “ice,” “grind,” and “filter” to confirm that your content covers the topic in-depth and provides value to searchers. 

As Google’s search algorithm becomes more discerning, it prioritizes content that sounds more natural. In the past, content creators might have used keyword stuffing to make their content appear more relevant to specific search queries. Now, Google evaluates relevance by more holistically judging the content on the page. 

By design, this shift penalizes pages that use spammy SEO practices and rewards high-quality content that aligns with Google’s mission. As such, keyword research services build semantic keyword themes into strategic SEO campaigns.

Is LSI Important for SEO?

No. Because search engines don’t use LSI technology. But semantic keywords are an important part of a strategy that can move the needle on your SEO goals

Using Related Words & Phrases: SEO Best Practices

Using keyword research to establish semantic keyword groups can form the cornerstone of a great SEO strategy.

Here’s what you need to know about finding related terms and using them to create topical relevance on your pages.

1. Use a Semantic Keyword Generator

I recommend using the ironically-named LSIGraph for a quick, free search for related keywords on a given topic. Click on any given keyword in the results to drill down into more keywords related to it.

screenshot of LSI graph showing semantically related keywords to cold brew coffee.

2. View Autocomplete Results

When you start typing in a search query, autocomplete results drop down from the Google search bar. Use what you find to round out your keyword group and narrow in on search intent.

Google autocomplete showing popular searches related to cold brew.

3. Check Out Related Searches

Similar to autocomplete results, related searches offer insights into keywords you might have missed.  Sometimes they can be used as clues for entities, phrases, and topics that might be worth mentioning in your LSI content writing efforts.

You’ll find related searches at the bottom of the page when you execute a Google search query.

Google related searches showing possibilities for semantically related keywords.

4. Know What Your Competitors are Using

SEMrush offers a free keyword gap tool that makes it simple to compare what keywords your competitors are ranking for versus your domain. The free option will only compare keywords at the domain level, but a paid subscription will get you access to page-by-page comparisons. 

In a Nutshell — LSI Keywords Are Semantic Keywords

Remember, whenever you hear someone talking about LSI keywords, they’re actually referring to semantically-related keywords.

Although Google doesn’t use LSI technology to power its search engine, using related phrases in your content will help it more accurately decode the meaning and value of your pages, winning you a better position in search results.

If you could use an assist with keyword research services, our SEO agency is here to help. Book a free SEO consultation, and let’s talk about how to get your website the attention it deserves.

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