“Hotseat” describes a way of computer gameplay, which requires (all) involved players but at least two human players to play on the very same computer, using the same input interface. (But not necessarily the same device, e. g. two USB keyboards can be used, still sharing the same key bindings.) This usually requires the players to switch their place or pass the keyboard during play. A popular example is Worms, where various players can play on the same computer one after another. UFO2000 on the other hand, is only for two players but doesn't even have bot support. But you play one player after another, seeing the moves of you opponent, when it is your turn. On top of the hotseat play, most of those games also support LAN or online play, very often singleplayer as well. There are, however, pure hotseat games, e. g. Warlords 1.