I remember learning about crater lake waaaay back in university geology, because the way the prof started talking about it was always absurd.

"Crater Lake is not actually a crater, its a caldera. A caldera is a special type of crater..."

"So you're saying its a crater."

"It's a caldera."

"...which is a type of crater."

"Yes but on a test you have to pick caldera from the options."