When used as a noun, fair refers to a traveling show with games, rides, and farmers showing off their prized pigs, similar to a carnival. As an adjective, it gets a bit trickier.
The adjective fair, has several different meanings. If someone says, "That's not fair!” they mean whatever happened wasn't just or done in an unbiased way. If you have fair skin, you have a pale complexion. If the weather is fair, it's a gorgeous day out. If the rides at the fair were fair, then they were just so-so. And watch out if the umpire shouts "fair ball!" during the baseball game — that means it was hit within the foul lines.