Elastic Stack consists of Elasticsearch, Logstash, and Kibana.
Elasticsearch is a distributed, real-time search and analytics engine that is used to store and index log data.
Logstash is a data collection and processing pipeline that ingests log data and sends it to Elasticsearch.
Kibana is a user-friendly visualization tool that allows you to interactively explore and analyze the log data in Elasticsearch. Hadoop is not a component of Elastic Stack.