Where did the word supercalifragalistic come from, and what does it mean?

The word originated from the 1964 Disney musical film called Mary Poppins which was written by the Sherman Brothers, and sung by both Julie Andrews and Dick Van Dyke. The word was made up to as something to say when you really don't have anything to say, but it is also used in other instances when someone wants to describe something as being great or really good.