This stands for "One-Night-Stand" and is used by some males to inform thier friends what they think of certain women in the club.

Onslaught, a game mode in Unreal Tournament 2004 where players trying to capture nodes to eventually make way to the enemy base and try to destroy the power core.

ONS is an abbreviation for "Over Night Studying", SON can also be used in some occasions. It is an action held by most, if not all, petroleum engineering students. It has been well known through out time, that this habit is to be practiced before major exams, and even quizes. According to new Petroleum engineering students, ONS is a sacred retual, that every -successful to be- engineer should experience!

Overactive neck syndrome

On Satan. Instead of saying On god you say On satan.