My GUESS is that means the amount of qualified overtime. Next year, the 2026 W-2s will have Box 12 with code "TT".
Check your last pay stub to see if the "TT" amount is reasonable close to the extra "half" amount (the 50% extra for overtime, not the base pay) of overtime that you were paid (only count overtime paid for over 40 hours, not overtime for other reasons). If it is reasonable close, that is probably what it means.
*IF* that is what it means, for Box 14 just select "other". But then be sure to answer the questions about overtime.
