Elasticsearch is a distributed, scalable, real-time search and analytics engine. It enables you to search, analyze, and explore your data, often in ways that you did not anticipate at the start of a project. It exists because raw data sitting on a hard drive is just not useful.
Elasticsearch allows search over large volumes of documents. It can easily scale to use multiple computers. Unlike traditional database systems, Elasticsearch is designed to deal with human language, which requires a certain degree of context awareness of the text corpus being searched.