Mud or MUD can refer to one of several things:

• A liquid or semi-liquid mixture of water and soil, or sediment, is commonly referred to as mud. Geologically speaking, mud is a mixture of water and particles of silt and clay. Ancient mud deposits harden over geological time to siltstone or mudrock (lutites ). See drilling rig for specific mud usage in oil drilling.
• A mud bath , possibly with special ingredients, is sometimes applied for beauty, health, or pleasure.
• Wet stucco or cement is often referred to as mud by contractors and cement workers, due to its texture's resemblance to mud. See also: slurry, Wet and messy fetishism.
• The British glam rock band Mud formed in 1968 and best remembered for their single Tiger Feet
• In relation to computer games, see Multi-User Dungeon
• In the game of contract bridge MUD is a defensive signalling convention that stands for Middle-Up-Down. A defender who plays his cards in this order is better able to communicate to his partner the number of cards he holds in the suit. The partner is thus able to infer the complete distribution of the suit.