Definition
A ceiling fan in a bathroom
How People Actually Use It
1. The proper name of the bathroom exhaust fan. It's purpose is allow moisture and smells to vent, prohibiting mildew growth, and nauseous guests.
"Kevin: Becca, there is no fart fan downstairs, you have to use the bathroom upstairs if you need to take a dump. Becca: I'm good, thanks."
Source: Urban Dictionary