Abbreviation for either Potentially Unwanted Application Classification used by anti-malware
software vendors for software which is not purely malicious like a computer
virus or worm but performs undesirable activities such as tracking users or activities of questionable benefit
, such as speeding up the system by an order of magnitude.
Alternately, might stand for Potentially Unsafe Application, a class of programs which perform legitimate activities in the hands of certain personnel, but can be abuse for malicious activity.