Loo/luː/ Definition 1 of 3Pro Tip 1/3British Slang Remember 'loo' is British slang for toilet, less common in other English-speaking countries. When I visited London, I asked where the loo was. Pro Tip 2/3Informal Use 'Loo' is informal and usually used among friends or in casual settings. I'm just popping to the loo, back in a minute. Pro Tip 3/3Conversation Break Saying you need the loo is a socially acceptable way to excuse yourself. Excuse me, where’s the loo? I need a quick break.