Final answer:
The Moscow Mule is the cocktail served in a mule mug, made with vodka, ginger beer, and lime juice, and it is known for being served in a distinctive copper mug.
Step-by-step explanation:
The cocktail that is traditionally served in a mule mug is the Moscow Mule. This refreshing drink is made with vodka, spicy ginger beer, and lime juice, garnished with a wedge or slice of lime. It is well-known for being served in a distinctive copper mug, which enhances its cold temperature and adds to the drinking experience. The use of a mule mug is a signature aspect of this cocktail and helps to distinguish it from other drinks.