Definition of "subfloor" [subfloor]

• The floor structure supporting and underlying the visible flooring or other finishing surface such as a carpet (noun)

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• "What you refer to as the subfloor is more accurately called the underlayment."
• "The particleboard underlayment is nailed to the subfloor, which is made up of beefier material, often plywood."
• "If you're interested in adding to your new vocabulary, the plywood fastened down to the floor joists is the "subfloor," and the wide boards above where the windows are going are the "headers.""