When taking the ball out the defender can say, "check" (throw me the ball, and I'll give it back... typically to make sure everyone on defense is ready)... If the offense (guy taking the ball out) says, "three feet, no check" before the defender says, "check", the defender don't get to check the ball and he/she needs to back up at least three feet.
This term is used a lot when playing street basketball to imply that you shouldn't get to close to the person you are trying to block. Me and my friends say it when someone you're talking to gets to close to you or is invading your personal space.
A girl is at a bar and a guy walks over to her to make a conversation by getting really close to her face with his face and his breathe really stinks.
Guy:"Hhhhhey beautiful. Hhhhhhhow are you tonight?"
Girl: "Hey man! Three feet no check!" (As she puts her hand out and pushes him out of her face)
An anarcho-communist movement by women , mainly on Snapchat, also on Instagram stories, who have to show their feet for shoes or pedicures but are not willing to show the men watching said photos uncensored, without a fee.