An acronym that is widely used to stand for the sarcastic expression 'Situation Normal: All Fucked Up'. It is a well-known example of military acronym slang. It means that the situation is bad, but that this is a normal state of affairs. The acronym is believed to have originated in the United States Marine Corps during World War II.
"What's the current situation in there?" "It's a real SNAFU. Everything is literally on fire." "So, same as usual."