The term 'titan' is used in many games to refer to something huge and impressive. It's almost always a metaphor for the godlike monsters of Greek Mythology.
Dungeons & Dragons
See Titan (D&D) for relevant information.
In Warhammer 40,000, Titans are gigantic warmachines. They come in Big, Bigger, Bigger than the Last One, Damn that's One Big Mecha, and XBAWKS HUEG (fucking massive).
They also tend to fuck up your shit.
There is also a moon called Titan in the Sol System. This is where the Grey Knights' highly classified fortress-monastery is, though for most of the Imperium it's just an annoying area of restricted voidspace right in the middle of the Imperium's second largest naval base - the Saturnian moon system. Malcador the Sigillite once moved this planet to the Warp for one year, using nothing but his own mind.
A wargame of recruiting monsters so you can recruit bigger monsters, and then catching up to other player's stacks of monsters so you could fight it out on sub-maps. You want to find and kill your opponent's "titan" monsters, which are as powerful as how many points that player has acquired so far. A classic of the monster slug-a-thon genre of boardgames. Someone made a flash version, which is Awesome.
In Mechaton Titan, "Titans" are the largest class of unit that can be made. We're talking LEGO giant robots that are bigger than your head.