What does "discharge battery" mean in a camera?

Question

what is that action?

Answer 1

take the battery out

Answer 2

It's good to discharge batteries fully before charging them again. And that's what it's doing.

Answer 3

take the battery out of camera

Answer 4

Lemmi is right: To avoid the "memory effect", every once in a while, rechargeable batteries should be discharged completely. The "memory effect" lowers the charge that the batteries can hold, so the power will drain faster and faster, until the batteries cannot be used at all anymore.