What are those things called that let you turn a regular bicycle into a stationary one for awhile?

Question

it's like a little triangle that boosts the back of your bike up off the ground for awhile

i've been trying to search with no luck, i guess because i don't know what they're called ... thankyou

Answer 1

Flat tires do that, but they aren't triangular.

Answer 2

cinder blocks

Answer 3

Stationary trainers.