Generally, when someone is writing a piece of code to demonstrate something, they will choose meaningless variable names, simply because the name is not important, but the logic of the code is.

I believe the origin of the words date back to a World War 2 US army expression "fubar" - f**ed up beyond all recognition - and hence we get two names, "foo" and "bar". Baz just jumped in the jeep and came along for the ride.