Latent Semantic Indexing (LSI)
Latent semantic indexing, or LSI, is a method for matching searches to documents that a team of researchers, most of them at Bellcore, a phone company research lab, described in 1990. It studies which words tend to show up together across a set of documents, then uses those patterns to pick out the documents that fit a search.
Source: Deerwester, Dumais, Furnas, Landauer and Harshman, Indexing by latent semantic analysis, Journal of the American Society for Information Science (1990), checked October 29, 2026
What Latent Semantic Indexing (LSI) means for your business
In SEO, the name lives on as "LSI keywords": lists of related words you're told to work into a page so Google sees it as relevant. Google's John Mueller has said plainly that they don't exist. On July 30, 2019, he wrote on Twitter, "There's no such thing as LSI keywords," and that anyone saying otherwise "is mistaken, sorry." That's one Google employee's public answer, not a written Google policy.
Google's guide to its ranking systems names RankBrain, BERT and neural matching as the systems that match a search to pages by meaning, and doesn't mention LSI. Its starter guide counts forced repetition, even of word variations, as keyword stuffing.
The 1990 method itself was a piece of math. The paper builds a large table of which words appear in which documents, boils it down to about 100 underlying factors, and compares each search to the documents in that reduced form. Nothing in it tells a writer which words to add to a page, and the SEO tools that borrowed the name hand you lists of related words instead.
Related words still belong on a page when a buyer needs them. A page about roof repair will talk about leaks, shingles and flashing because that's what the customer is asking about. We'd skip the keyword list and write for the questions. If someone sold you LSI keywords and your pages still don't rank, writing pages around what buyers ask is the work we'd do instead.
Source: John Mueller on X, July 30, 2019, checked October 29, 2026
Last reviewed October 29, 2026. All terms
How AI answers it today
On October 29, 2026, Google's AI Overview cited Wikipedia, a search software blog, Stanford's textbook and YouTube, and called LSI keywords a myth Google doesn't use. ChatGPT, citing nothing, said Google doesn't use LSI to rank pages today.
Our run through ChatGPT and Google's AI Overview, October 29, 2026. A sample, not what every buyer sees.
Related terms in crawlers and technical access
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