Elasticsearch is a scalable full-text search engine that allows users to search content and metadata and perform analytics. It features complex query options, attribute and geo filtering, and built-in analytics and tag clouds. Elasticsearch is special because it is distributed, allowing easy clustering of data across multiple servers. It can also scale performance independently for indexing and searching, and handle complex queries on billions of documents even with just a few nodes. Elasticsearch also has an easy built-in backup solution.