an alphabetical list of words relating to a specific subject, text, or dialect.
Latent Semantic Indexing (LSI) is an indexing and retrieval technique in which a site's central theme is looked at rather than any specific keyword.
In latent semantic indexing, Google sorts sites on the frequency of a variety of terms and key phrases linked together instead of the frequency of a single term. The contents of a webpage are crawled by a search engine and the most common words and phrases are put together and identified as the keywords for the page. LSI also looks for synonyms related to the title of your page.
The objective of using LSI is to tell Google spider how to index your content based on your intent. It can improve your search rankings when you help Google understand the topic you’re writing about and how relevant it is to the search query.
LSI do's include: use of keywords in content (primary, secondary, synonyms), page title and heading tags.