  With the ever increasing size of the web, relevant information extraction on
the Internet with a query formed by a few keywords has become a big challenge.
Query Expansion (QE) plays a crucial role in improving searches on the
Internet. Here, the user's initial query is reformulated by adding additional
meaningful terms with similar significance. QE -- as part of information
retrieval (IR) -- has long attracted researchers' attention. It has become very
influential in the field of personalized social document, question answering,
cross-language IR, information filtering and multimedia IR. Research in QE has
gained further prominence because of IR dedicated conferences such as TREC
(Text Information Retrieval Conference) and CLEF (Conference and Labs of the
Evaluation Forum). This paper surveys QE techniques in IR from 1960 to 2017
with respect to core techniques, data sources used, weighting and ranking
methodologies, user participation and applications -- bringing out similarities
and differences.
