slang Short for McDonald's, an international fast food restaurant chain. Can refer to one of their restaurants, the food that they serve, or the company as a whole. I'm heading to the McD's across the street after class, do you want a burger or anything? Well, it's no wonder you've been putting on weight—you've been eating McD's every day for the last six months! I heard that McD's is looking to buy up yet another fast-food chain.