Single-player

From Styleguide

single-player

A game designed to be played by a single person.

Only refer to a game as a single-player game if it offers no multiplayer modes whatsoever. Otherwise, refer to a game's single-player mode or the single-player portion of a game.

Example: If you really want to see Ubisoft's Ghost Recon: Advanced Warfighter shine, you'll need to ditch the static single-player experience and try the game online.

Wrong: one-player, single player.

Also see: mode, multiplayer.