SNAFU is an acronym that stands for Situation normal: all fucked up. It is sometimes bowdlerized to Situation normal: all fouled up or similar. In simple terms, it means that the normal situation is in a bad state, as it always is, therefore nothing unexpected. It's usually used in jest, or as a sign of frustration. The acronym is believed to have originated in the US Army during World War II.
In modern usage, snafu is sometimes used as an interjection. Snafu also sometimes refers to a bad situation, mistake, or cause of trouble. For example, in 2005, The New York Times published an article titled "Hospital Staff Cutback Blamed for Test Result Snafu".