Latent Semantic Indexing (LSI) is a mathematical technique that refers to the approach of evaluating words not only on their own, but also together with the related words around them. In the SEO community, the term “LSI keyword” is used for words that are semantically related to the target keyword.
An important note: Google has not officially confirmed that it uses LSI as a ranking signal. In fact, Google spokespersons have occasionally said, “there is no such thing as an LSI keyword.” Instead, Google uses far more advanced NLP models such as BERT and MUM.
Still, the “LSI keyword” approach is useful in practice:
- Including related concepts in content to cover a topic in depth
- Using natural synonyms instead of keyword repetition
- Building topical authority
Tip: Instead of thinking in terms of LSI, think of it as “covering the topic comprehensively.” Look at the SERP for a keyword, and include the questions in the “People Also Ask” box and related searches in your content. This is the modern semantic SEO approach.