How does cel-shading in games work?

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For those of you familiar with the likes of Zelda: Wind Waker, Auto Modellista, or Jet Set Radio, what exactly is going on when a game is given the 'cel-shaded' look? This type of artistry within games interests me, and I'd like to know a little bit more about how it's accomplished.

Any useful links you guys know of that describes how this look is acheived?