Used to indicate a person or thing whose name is not known or can't be remembered. "What do you" is often condensed into informal contractions such as "whaddya" or "what d'you," and the phrase is sometimes hyphenated in writing. I heard old what do you call him is back to teaching the course again next week. I ran into whaddya-call-her from next door down at the grocery store this morning. He keeps playing that dang what-d'you-call-it on the computer all day.