Plain English Meaning
The FAA's old rulebook for what a pilot had to do, and how well, on the flight portion of a checkride. It is being phased out and replaced by the ACS.
Full Definition
An older FAA publication that set out the required tasks, knowledge areas, and performance criteria an applicant had to meet on a practical test (checkride) for a pilot certificate or rating. The PTS has been progressively replaced by the Airman Certification Standards (ACS), which combines the same task and skill requirements with the matching knowledge test areas in a single document.
Context Anchor
Seen in FAA training and when discussing how pilot applicants are evaluated, especially when comparing older with the newer Airman Certification Standards.