A subfloor is the supporting layer of a floor, typically made of plywood or concrete, that lies directly underneath the visible flooring materials. However, there are a few synonyms for this essential component. Some alternatives to the term "subfloor" include "underlayment," "base flooring," or "foundation layer." These expressions speak to the crucial role that this layer plays in providing stability, insulation, and protection for the top floor covering. Whether referring to it as a subfloor, underlayment, or base flooring, the fundamental purpose remains unchanged – to create a solid and sturdy base for the rest of the flooring structure.