[from the HTTP error "file not found on server"]. Extended to humans to convey that the subject has no idea or no clue -- sapience not found. May be used reflexively; "Uh, I'm 404ing" means "I'm drawing a blank".
404 compliant: adj.
The status of a website which has been completely removed, usually by the administrators of the hosting site as a result of net abuse by the website operators. The term is a tongue-in-cheek reference to the standard "301 compliant" Murkowski Bill disclaimer used by spammers.