Word commonly used by teenyboppers in IM conversations even though they have no clue what it means.
Some guy: Hey, whats your phone number?
Some guy: What the fuck is an idk???
Teenybopper: I dont know
Some guy: If you dont know what it means then why the hell did you say it??
Teenybopper: Uhh.... (Teenybopper has signed off at 14:42)