Does the Short-Term/long-Term Distinction Apply to a Professional Trader?

Yes, the distinction applies unless the professional trader makes the Section 475(f) mark-to-market election. Without the 475(f) election, the trader's capital gains are still categorized as short-term or long-term based on the holding period.

With the 475(f) election, all gains and losses are treated as ordinary income or loss, and the distinction is irrelevant.