(fandom slang) The television show Doctor Who.

plural of who; often used along with whats, whys, hows, etc.

A rhetorical question asked to show that the person asking it neither knows the answer nor knows who might.

(colloquial, rhetorical question, sarcastic, humorous) Used as a retort or comeback, often to deprecate oneself or another for excessive concern or attention to detail.

(colloquial, rhetorical question) A reply to an unimportant or irrelevant statement, indicating indifference on the part of the speaker.

(colloquial) Who says so; on whose authority?

Asks the interlocutor for their identification

Used by a phone-call receiver to ask the identity of the caller.

(defensively) Used to ask a stranger asking a question to identify themselves

(informal) A marathon of the British science-fiction series Doctor Who.