And when ATSs are used, a resume that doesn't have the right combination of keywords may never be seen by human eyes.

An ATS is a software system and a database holding resume information. It operates behind the commercial and corporate job boards to capture and store submitted rsums.

When a resume is submitted through a job board, the content is separated and placed into the ATS. The resume loses all of its formatting and becomes plain text within the database. This is why it's best to use a plain-text (ASCII) version of the resume when submitting through job boards, so it's easier for the ATS to work with.

Employers sign on to the ATS and perform keyword searches. For the resume to reach human eyes, it must contain keywords matching the search criteria. When there's a decent match, the employer can choose to view the entire rsum.