FrameArray will be a member of the CMotion class. That simply means that the member should be default-constructed. Since that's what would normally happen anyway, putting it there is redundant, but doesn't hurt anything.

If would be meaningful if FrameArray's class didn't have a default-constructor, so you had do do something like
Code:
CMotion::CMotion(void) : FrameArray(0)
in order to compile.