As acronyms the difference between mud and fud

is that mud is an interactive online environment in which players may jointly engage in fantasy role-playing games while FUD is Fear, uncertainty, and doubt, a marketing strategy involving the spread of worrisome information about a competing product.

As nouns the difference between mud and fud

is that mud is a mixture of water and soil or fine grained sediment while fud is alternative case form of FUD.

As a verb mud

is to make muddy, dirty.