A combination statistic to represent a character's intelligence in terms of ability to reason, grasp and resolve complex issues and problems, and overall mental capacity. It's not necessarily speed, as that's more reflected in the wits statistic. As a scale:
0: All the intellectual horsepower of a particularly stunted cabbage.
1: The proudly, aggressively dumb. The individual that fervently supports the cause you find most odious.
2: The dead average of human intelligence, which means they typically consider themselves quite smart.
3: For some, they are just smart enough to be really pretentious about it. Likes to quote philosophy of questionable relevance to the topic at hand.
4: The evil genius type clever enough to come up with an exceedingly complicated plan that happens to have a fatal flaw.
5: Doesn't have the fatal flaw.
6: "I should thank you. I'd almost forgotten the excitement of -not- knowing. The delights of uncertainty."