A phone number that used to be yours and is now someone else's; conversely, a phone number that used to be someone else's and is now yours.
Me: "Someone kept texting that he loved me and finally I said 'WHO THE HELL ARE YOU?' and then his mom said it was a kid and this used to be his dad's number. I felt bad."
Friend: "That's what happens when you have a regifted phone number."