What does $C_c^1((a, b))$ stand for?

Question

What does $C_c^1((a, b))$ stand for?

I know that $C^1((a, b))$ is a space of functions with the continuous first derivative on $(a, b)$, but I don't know what the small $c$ stands for.

Answer 1

Continuous differentiable functions with compact support. That is, continuous differentiable that vanish on all but a compact set.