LSI Stands for Latent Semantic Indexing it is answer of search engine(Google) to regular keyword stuffing of many spammy websites in the world. Webpage are crawled by a search engine and the most common words and phrases are combined and identified as the keywords for the page. In LSI approach , search engine not only uses meta tags and keywords appear, but it also looks for synonyms related to a particular word, and assign it as your webpage keyword and rank it higher than other sites competing for the same keyword.