Elasticsearch is a distributed, open-source search and analytics engine designed for fast, real-time searching of large datasets. It is commonly used for full-text search, log analysis, and real-time data monitoring, providing near-instantaneous results by indexing data as it's ingested. Built on top of Apache Lucene, Elasticsearch is highly scalable and allows for powerful queries, filtering, and aggregations. Its flexibility and speed make it popular for applications like search engines, data analytics, and logging systems like the ELK stack (Elasticsearch, Logstash, Kibana).