Elasticsearch is a search engine based on the Lucene library.
It provides a distributed, multitenant-capable full-text search engine with an HTTP web interface and schema-free JSON documents.
Elasticsearch is developed in Java and is dual-licensed under the source-available Server Side Public License and the Elastic license, while other parts fall under the proprietary Elastic License.

Shay Banon created the precursor to Elasticsearch, called Compass, in 2004.

Elasticsearch can be used to search any kind of document.
It provides scalable search, has near real-time search, and supports multitenancy.

"Elasticsearch is distributed, which means that indices can be divided into shards and each shard can have zero or more replicas.

Each node hosts one or more shards and acts as a coordinator to delegate operations to the correct shard(s).
Rebalancing and routing are done automatically".

Related data is often stored in the same index, which consists of one or more primary shards, and zero or more replica shards. Once an index has been created, the number of primary shards cannot be changed.

Official Website :- https://www.elastic.co/elasticsearch/