Elasticsearch is an open-source search engine that uses Lucene to index and search large volumes of text data quickly. It operates based on the inverted index technique, where documents are indexed by their terms, allowing efficient retrieval. When a query is made, Elasticsearch compares the terms in the query with the terms in the indexed documents and ranks them according to relevance.
Elasticsearch supports full-text search, filtering, and advanced search features like faceting, which groups results based on certain attributes. It also supports fuzzy matching, stemming, and synonyms to improve the quality of search results.
Elasticsearch can handle large-scale datasets and is horizontally scalable, meaning it can distribute data across multiple servers. It is widely used for log analysis, e-commerce search, and as a backend for various applications requiring fast search capabilities. It is also part of the Elastic Stack, which includes Kibana (for visualization) and Logstash (for data collection).