I've learned that by making variants of a block, or reusable object like a wall, that if you were to make one set that's missing the left side or one that's missing the right side, this lessens the memory usage for that particular object. Say you have to blocks sitting side by side, the camera isn't going to see the two sides in between them so you replace them with the blocks that have a missing side for efficiency.
My question is: What is this method/procedure called?
Not quite, it's not automatic like backface culling. I'm talking more about making various versions of a particular object with different sides missing.