An applicant tracking system, also called a candidate management system, is a software application designed to make recruitment process for enterprises easier and efficient.
An ATS should be able to handle the process of recruitment end to end. It can be used to do job posting, screen and filter job applications or resumes, place an interview request, hire and on-board an employee etc.
More information: http://www.recruitingblogs.com/profiles/blogs/applicant-tracking-system-ats-how-to-start-with-one