That's what I would say is correct, and that may be the proper term for that piece of wood or metal that seals the door at the bottom that one steps over...But my relatives in the Midwest would say the threshold is the part of the porch where the doormat is, as in "She looked out the window, and standing on the threshold, out in the rain, was a fellow who called himself The Dapper Hooligan." More @Wikipedia
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