This is a hilariously broad category that could almost include anything that exists. But I think form especially is only partially understood. Ask designers to identify and describe good form and function and they will predictably pick an Eames’ chair, a Mies van der Rohe building, or a Shaker box. But the concepts are much grander.
Form hovers somewhere at the intersection of function and context, and exists in all works of design, even if they are not visual. Music has form, as does literature and movement and smells and people and public space. Form has a kind of majesty, and it is often easier to see in simple things.