What does std::_Bind

I'm trying to make sense of what this means in my compiler debug output:

std::_Bind<std::_Mem_fn<void (ClassName::*)()>(ClassName*)>

If it matters, it's being used as the value for a template variable that's being used as the type for a class member variable.

The bit I know I'm not sure of is "ClassName::*" (Google is really bad when the important bit of what you're searching for is the non-alphanumeric bit)