OOs

Balls, as in testicles. Also, big balls.
The strength or stupidity to make hard decisions or do courageous things.

Greece is winning, because Europe doesn't have any OOs (Alice - 14/06/2015)
Man, it took some OOs to face up to that angry mother.
He was kicked in the OOs and went down screaming.
(used in written text only, not in speech - multi-lingal)

Oos

Cannabis, Weed

Hey, hast du das oos?

Yea bro!

OoS

Oath of silence.

Just a shorter way of typing out Oath of silence.

OoS means "Not talking for a long period of time"