Latent Semantic Indexing (LSI) is a system used by Google and other major search engines. The contents of a webpage are crawled by a search engine and the most common words and phrases are collated and identified as the keywords for the page. LSI looks for synonyms related to the title of your page. For example, if the title of your page was "Classic Cars", the search engine would expect to find words relating to that subject in the content of the page as well, i.e.