Elasticsearch
In plain terms
A distributed search and analytics engine.
Going deeper
Elasticsearch indexes data for fast full-text search, filtering, and analytics at scale, often for logs and search features. It's built on Apache Lucene.
Under the hood
Inverted indexes enable fast search; the ELK stack pairs it with Logstash and Kibana for observability.
Examples
Site search, log analytics (ELK), observability, full-text search, dashboards.
Think of it like...
Like a super-fast librarian who instantly finds every document mentioning a phrase.