Jenkins is an open source Continuous Integration tool that monitors execution of repetitive jobs, such as building a software project or jobs ran by cron. It’s written in Java programming language and designed to test and report on isolated changes in a larger code in real time.
It is Originally started as Hudson in 2004 but due to a dispute in 2011 they forked and continued under the name, Jenkins.
It can be used to build software, deploy software, or websites to various endpoints or to run unit/behaviour-driven software tests.
So the builds on top of Continuous Integration are Continuous Deployment and Delivery where after the successful tests you will be able to run, instantly and automatically release with the latest version of your codebase. We can say Jenkins makes deployment a non-issue and helps you speed up your development.
Basically, we can say that “Jenkins is a Continuous Integration server which is the best practice of running your tests on a non-developer machine.”