Or skill?  It matters because many anti-gambling laws have exceptions for games of skill.  From an article in the LA Times:

Other recent skirmishes include a South Carolina case in which five men were arrested in a 2006 raid on a game of Texas Hold ‘Em. They were convicted this year by a municipal court judge who said that he agreed that poker hinged on skill, but that he thought it wasn’t clear whether that was relevant under state law. The men are appealing their convictions.

In Columbia County, Pa., a judge dismissed charges in January against a man accused of running a poker game out of his garage, ruling that he hadn’t committed a crime because when skill predominates, it’s not gambling.

But in a second Pennsylvania case, a Westmoreland County jury last month rejected a man’s contention that the Texas Hold ‘Em tournaments he hosted in local fire halls were legal because they were games of skill.

Can you give an operational definition of a game of skill?  Is tic-tack-toe a game of skill?  (a bit of trivia:  I once bet Matt Rabin I could beat him in 5 games of tic-tack-toe out of 50.  I won the bet.)  Is rock-scissors-paper a game of chance?

Trilby Tilt:  The Volokh Conspiracy.