Basically an even cooler way to say "cool." Can also refer to a place, be a conversation urger, or something to say when you have no idea what the other person is talking about. May have originated around the '50s, brought back by the movie Ghost World.
girl1: 8 mile is such an awesome movie!
boy1: yeah, coolsville.
boy2: Wanna go to the bowling alley tonight?
girl2: that place is coolsville!
teacher: we're going take the heterozygus allel for constricted pods and the homozygous allel for white seed color. aren't genetics fun?!?
A fictional place coined by singer/songwriter Rickie Lee Jones in 1979. Coolsville is largely populated with colorful characters both hopeless and hopeful, the disenfranchised, the down-and-out, hipsters, bohemians, junkies, artists, and what not. Coolsville is a place of hard redemption. It can also be used as an adjective and verb.
"The real thing come and the real thing go/The real thing is back in town/Ask me if you want to know the way to Coolsville." - Rickie Lee Jones