“Elasticsearch is a distributed, search and analytics engine for all types of data.”
Long time users of elasticsearch are probably using it for the full text search capabilities, meaning it generally powers a search function in an application. And since it’s not limited to text, it can even be used as the main database. A more popular use case is probably storing and searching logs: the famous ELK stack.
Our first use case was logs as well. We had moved most of the applications to our private cloud and limited the number of people with access to production machines, and suddenly developers were unable to reach their precious logs. Since copying log sections around wasn’t a real solution, we deployed ELK stack to collect all logs in a single system. Everyone loved the idea even though Kibana v2 was leaving a lot to be desired. On another project we used elasticsearch for rapid indexing to power a leaderboard-like usage. In short it is a versatile technology, and with the extra tools like Logstash, it’s in a pretty unique position.