Probability of success

Part of speech, the role that a word or phrase plays in a sentence

Polycystic ovary syndrome, a disease of the ovaries

Pain of Salvation, a Swedish progressive metal band

Point of sale, the location where a business transaction occurs

Piarco International Airport (IATA airport code: POS)

P/OS, the Professional Operating System sold by Digital Equipment Corporation for their PRO-300, PRO-350, and PRO-380 PDP-11-compatible line of personal computers

SNCF TGV POS, a French high-speed train

Post Office Sorting Van, a type of rail vehicle used in a Travelling Post Office train

Parent over shoulder internet slang.

Packet over SONET/SDH, a communications protocol for transferring packets over fiber networks

Programmable option select, the predecessor to plug-and-play

Proceedings of Science, an electronic publishing service for proceedings of scientific conferences

Point of service plan, a type of health insurance in which patients choose their doctor and he/she will be their "point of service"

EFTPOS or POS Terminal, a device by which sales transactions can be directly debited to the customer's bank account

Pomona (Amtrak station), California, United States; Amtrak station code POS.