An applicant tracking software (ATS), also called candidate management system or recruitment system, is a software application designed to help an enterprise recruit employees more efficiently.
Wikipedia defines as "An applicant tracking system (ATS) is a software application that enables the electronic handling of recruitment needs. An ATS can be implemented on an enterprise or small business level, depending on the needs of the company. An ATS is very similar to customer relationship management systems, but are designed for recruitment tracking purposes." You can read more here (http://en.wikipedia.org/wiki/Applicant_tracking_system)