Portal (InstanceTopic, 3)
From Compile Worlds
A portal does nothing on its own, but in pairs (portal pairs), they allow any object, including you, to move into one and out of the other with the same speed.
Portal also refers to the game in which you must think with portals. The reward for this game is delicious cake. There have been 2D and 3D versions of this game, though only the 3D one is official.
A portal puzzle is a thread commonly posted on imageboards where people try to solve a puzzle using portals. They are usually subtle and vague, to encourage humor.