Consider the following image (img_1)
I guess the whole thing is called a floor framing system and subfloor is a part of the system. So subfloor is a part of floor. is my understanding right?
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Sign up to join this communitySubfloor is a part of the floor but has a different purpose. Without a solid sheet that spans the joints and the ends are supported, how can you install tile or wood flooring? In the oldest residential constructions I’ve seen, they used either two layers of thick wood planks (bottom acting as a subfloor) or boards run diagonally as the subfloor. Today, we almost exclusively see OSB, but the purpose is the same. It provides even support for the floor.
The subfloor is the support used so the final floor covering (the "pretty one - tiles or polished wood etc) is properly supported.