It's a ficticious word that you say when you want to sound precocious or when your tongue tied and need to come up with something impressive.
"George, what do you have to add to Christy's comments about your budget proposal?"
George, sweat visible now above his brow, fidgeted in his seat as he panicked at his obvious loss of words. Then a miracle happened; he opened up his mouth and said, "supercalifragilisticexpialidocious!"
"That's terrific. Rodger make sure George gets the money he's asking for. Wow, just great George. Christy you could learn from him."