Have you ever heard these terms - index term, subject term, subject heading, or descriptor in information retrieval. Basically this is a term which attracts the gist of the topic of a document. The function of index term is to make up a controlled vocabulary for use in bibliographic records. Well index term has a prominent role in libraries collection, organizing them and spread documents. Index term is uses as keywords to retrieve documents an any information system i.e. a catalog or a search engine. It consists of a word, phrase or alphanumerical term. They are created by analyzing the document either manually with subject indexing or automatically with automatic indexing or more sophisticated methods of keyword extraction. Index terms can either come from a controlled vocabulary or be freely assigned.