What does O.S stand for?

What does O.S mean?

OS	Open Source Computing » General
OS	Open Source Computing » Software
OS	Operating System Academic & Science » Electronics
OS	Operating System Governmental » Military
OS	Operating System Computing » Drivers
OS	Operating System Computing » Security
OS	Operating System Computing » General
OS	Operating System Computing » Software
OS	Operating System Governmental » NASA
OS	OStium (mouth) Medical » Physiology
OS	Old School Community » Educational
OS	Ordnance Survey Governmental » Military
OS	Online Services Computing » Networking
OS	Outer Space Governmental » NASA
OS	Old Skool Governmental » Military
OS	Open System Computing » General
Os	Osmium Academic & Science » Electronics
Os	Osmium Academic & Science » Chemistry
OS	One Size Miscellaneous » Clothes
OS	Overall Survival Medical » Oncology
OS	O Sullivan Community » Famous
OS	On Service Governmental » Military
OS	Old Style Community » Media
OS	On Sea Governmental » Military
OS	Off Screen Community » Media