I've managed to get into a situation where I have to come to a clear understanding of interior architecture. It would be my preference to avoid having to define this, but the circumstances are beyond my control. It is a human obligation to set arbitrary limits on things--we are after all, thoroughly linguistic in mental capacity. Dragons do not have fur.
It's not enough to say that interior architecture is the inside of a building. An open air stadium is an inside that is also an outside. The user experience is internal and boundaries have to be clearly established in order for spaces to function. Weatherproofing becomes a component of design.
The best I can come up with is that an interior architect has a greater degree of responsibility for internal adjacency, lighting, surface textures, color, and furniture.