Internal Loading is a strange term. Loading, in structures means applying moments or forces on a structure. I.e. loads are boundary conditions. By this rationale, Internal Loading means loads that are applied inside the structure, such as pretension.
However, most people use Internal Loading in a different sense: as an umbrella term for internal forces and moments arising in a structure due to a loading. This usage is confusing as cause and effect gets jumbled together. Hopefully, a better shorthand for "internal moments and forces" can be found.