Definition of a Hangover

Overheard at Liz's house last week, whose son had just celebrated his 19th with a rather alcoholic party.

LIZ: I bet there'll be a few hangovers here this morning.
ELLIE (11 year old daughter) What's a hangover?
LIZ: It's when people may be feeling rather delicate with a headache, when they've drunk too much alcohol.
ELLIE: Oh, I thought it was that bit that hung over the top of your jeans