A fastball in baseball lingo. It can also be used to describe a singular movement of increased intensity that is designed to bewilder another person.
Originally from the movie The Bad News Bears.
To shove, forcefully, a fully-engorged penis into someone's rectum. Without lube and without warning. Causing a sharp rise in pulse, blood pressure, and sweat.
Guy A: "Bro, did you ever tag that Emily bitch?"
Guy B: "Please. Dude, I fucking ran 'the heater' on her."
A firearm- Usually a handgun or revolver. This term came from the 30's mafia/gangster times. When continually fired, the barrel would get very warm- hence the name heater.
"Before we go out tonight, do you got your heater?"
Don't mess with her, she's got a heater.