Elasticsearch is a NoSQL database that is based on the Lucene search engine.

Logstash is a log pipeline tool that accepts inputs from various sources, executes different transformations, and exports the data to various targets. It is a dynamic data collection pipeline with an extensible plugin ecosystem and strong Elasticsearch synergy

Kibana is a visualization UI layer that works on top of Elasticsearch.

These three projects are used together for log analysis in various environments. So Logstash collects and parses logs, Elastic search indexes and store this information while Kibana provides a UI layer that provide actionable insights.