Expression of disappointment or disgust.
Oh foo - the cake burnt!
A popular name for a temporary file, function or variable, or an example of same in documentation. Often used with "bar" to create "foobar," which is a variation of FUBAR. FUBAR came out of World War II and means "F***ed Up Beyond All Recognition."
Origin of foo
Circa 1935 as nonsense word, circa 1960 in programming sense.