What is Jenkins?Jenkins is an open source continuous integration tool written in Java. It is a server-based system running in a servlet container such as Apache Tomcat.
Jenkins CI Server

It supports SCM tools including AccuRev, CVS, Subversion, Git, Mercurial, Perforce, Clearcase and RTC, and can executeApache Ant and Apache Maven based projects as well as arbitrary shell scripts and Windows batch commands. 

Builds can be started by various means, including being triggered by commit in a version control system, scheduling via a cron-like mechanism, building when other builds have completed, and by requesting a specific build URL.

Jenkins script use Groovy which is a java like scripting language via JVM.Groovy script is written at “Jenkins Console”.Plugins have been released for Jenkins that extend its use to projects written in languages other than Java.

Plugins are available for integrating Jenkins with most version control systems and big databases. Many build tools are supported via their respective plugins. Plugins can also change the way Jenkins looks or add new functionality.

Builds can generate test reports in various formats supported by plugins (JUnit support is currently bundled) and Jenkins can display the reports and generate trends and render them in the GUI.