Latent Semantic Analysis (LSA) or Latent Semantic Indexing (LSI) is a technique in natural language processing, in particular in vectorial semantics, of analyzing relationships between a set of documents and the terms they contain by producing a set of concepts related to the documents and terms.
LSA closely approximates many aspects of human language learning and understanding. It supports a variety of applications in information retrieval, educational technology and other pattern recognition problems
Generally LSA deals with the phrase matching. In a document Google just for the keyword synonyms and its related phrases.