LSI SEO, i.e Latent Semantic Indexing, 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 collected, combined and identified as the keywords for the page. In LSI approach, search engine not only uses meta tags and keywords appear several times, 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.