This is purely terminology we used internally.
Assembly Binding is the process of probing. A.k.a, given an assembly name, finding out where the assembly is. Assembly binding is performed by fusion. This also includes applying policy. Managed code is not run during assembly binding.
Assembly Loading happens after assembly binding, where CLR loader gets the assembly from fusion, and makes it available to managed code. Security policy is evaluated here, as well as the module constructor if any.
For the most people there is really no difference between assembly binding and assembly loading. But sometimes these two terminology confuse people in fusion team and CLR Loader team (Yes, we are different team.)