A number where the value is determined at the user's discretion. Subject to change every time it's used.
JIM: I bet you a snillion dollars that you can't toss that up and catch it in your mouth!
GINGER: I just did. You owe me a million dollars!
JIM: No, I said a snillion dollars. That's really only $1 dollar.
(Had Jim won the bet, he could have claimed that it was worth $10, $100 or any other value)