This is when your phallus is hard at the most inappropriate time (i.e. work, church, school, etc.) and you have to put it over your belly button and hold it with a belt. Word of caution: no hugs and don't dap up your homies where a partial hug might be given.
Mental conversation with yourself: "Man I hope no one notices my belty. I hope the teacher doesn't call on me to come to the board."
My penis was hard while I was getting ready for church so I decided to do a belty just in case.