Jenkins is an open-source continuous integration software tool written in the Java programming language designed to test and report on isolated changes in a larger code base in real-time.

Ramesh, great explanation.

http://searchsoftwarequality.techtarget.com/definition/Jenkins

Jenkins is an automated Build Server. It's integrated with Versions Control System(SVN,TFS) to build code.

Jenkins is an open-source continuous integration software tool used for testing and reporting on changes made by all the developers in a larger code base in real time. The software enables developers to find and solve defects in a code base rapidly and to automate testing of their builds.So we can make Jenkins to run periodically twice or thrice a day, which will fetch and merge all the changes made by developers and will run all the unit test created. With this developers can easily get the result of all the test cases whether the frequent changes made is breaking the build or not.