A term used when responding to a "thank you". It is a mixture of "no problem" and "I don't mind", meaning "don't even worry about it, because I'm not. It isn't even an issue."
This can also be used to tell someone they shouldn't worry about something in general.
Mike: "Yo dude, thanks for giving me a ride downtown. I owe you one."
Joe: "Oh, dude, no mind. It was just great to get out of the house."