Something that can be either bad, great, horrible, fantastic, or quizzical. There is an endless multitude of possible definitions for this word. Basically you should use this word in situations where you want to say something with a lot of syllables and want to sound fancy but yet be very vague.
"Get away from my baby, you quintillery of a man!"
"OUCH, MY QUINTILLERY FOOT!"
"Why is it so quintillery hot out, did Al Gore take off his pants?"