PMQs is a weekly event where MPs have half an hour to pin questions directly on the Prime Minister in the House of Commons, and get answers out of him. The leader of the opposition gets most questions, and other party leaders get more, with the rest being given to ordinary MPs (government ministers can't ask PMQs as far as I know). It's the most publicised bit of Parliament's business, and is where a lot of shouting, sarcasm and political theatre goes onn.