The technical term is
frenulum. Actually, if you're male, you have
two frenula. I leave it to you and google to find out about that (though you won't have to look far).
Yeah, after a long session of cunnilingus, my frenulum gets pretty darn sore. I've even been known to chew ice afterwards.
It's a frenulum. I'm not going to dignify the word "googler".