Slang for "welt". Used mainly in the southern part of the US. Has the same meaning as the word "welt". Raised white mark that appears after sustaining a smack on the skin. Usually appears in the middle of the red area after you have been slapped or smacked.
My Ma slapped my ass and left a welp in the shape of her hand.
I left a welp on her forehead when I smacked her with my cock.