A gluk is a slang term common among the IT personnel of Russian descent. Derived from the Russian word for hallucination, this word can mean any of a number of things, all of them generally undesirable, such as: a bug, BSOD, a mindfuck or a brain fart on behalf of the interlocutor, or any other non sequitur. Oh, as an afterthought on pronunciation: rhymes with "puke".