A character or account that appears to be new, but is actually being played by someone with a lot of experience in the game.

There are usually two reasons for a person 'smurfing'. First, it may be that the player has a certain reputation that they want to leave behind for a while, as it may get in the way of normal conversation and gameplay. Alternatively, the game in question may have matchmaking functionality that puts an experienced player against other experienced players. By smurfing, the game will think the player is new, and will therefore match them against other new players. This is generally frowned upon, as the smurf player will almost always win these games against newbies due to their advanced experience and skills.