What is the difference between an ATS ranking candidates and filtering them out?

Filtering removes or hides applications that fail a rule; ranking orders applications so some are looked at first. They are different, and many systems can do one, both or neither, depending on the product and the employer's settings.

• Filtering example: a rule that declines anyone who answers "No" to a required licence question.
• Ranking example: the system shows candidates whose profile seems closer to the job description higher in a list, or a recruiter sorts by a match indicator.
• Searching example: a recruiter types a skill and location and only sees profiles that contain them.

With ranking or searching, your resume is still in the system; it may simply be seen later or found under different terms. Clear job titles, honest relevant keywords and accurate answers help in all three cases.