"What is a 'ball'?"
"A ball is round."
"Then this is a ball?"
"No, a ball is 3 dimensional, that's a disc."
"Then this is a ball?"
"No, that's a cylinder. A ball is spherical."
"Then this is a ball?"
"No, that doesn't bounce. A ball is a sphere that bounces."
"Then this is a ball?"
"No, that's an orange. A ball is a sphere that bounces and is used in sports and games."
"Then this is a ball? It's round, bounces, and is used in a games and sports."
"No, that's a marble."
"Then show me a friggin' ball, then!"
"This is a rugby ball."
"But, but, it's not round!"
"But it is a ball."
"So a ball is round, bounces, and is used in sports and games, except for marbles, which aren't balls, and rugby balls, which are balls, but aren't round?
"You've got it."
"But what has any of this got to do with a dance?"
"What?"
"I've been invited to go dancing at a ball, and I was wondering what a ball was."