A word used to describe something awesome; cool; good; swanky; spiffy.
Person 1: I'm going to a concert tonight!
Person 2: Fancy!
Person 3: Awesome!
Person 2: No. Fancy. It's going to be fancy.
Person 1: No you don't have to get dressed up.
Person 2: NO YOU IDIOTS! Look it up on Urban Dictionary. Fancy just means cool or awesome. Come on guys, get with it.