O&S is the abbreviation of the duo bosses in the
game "Dark Souls", Ornstein and Smough, whom guard the Chamber of the Princess in Anor Londo.
This abbreviation is used by lazy
people, whom don't bother writing the full names when looking up guides on how to
beat them.
The O&S bossfight is sometimes referred to as the hardest and douchiest boss battle in the game.