What it is
Back pay restores lost wages after a finding of a violation, such as WARN per-day damages, unpaid overtime, or a wage claim. It is separate from front pay, which covers projected future losses. In settlement math, back pay is usually taxed as wages and reported on a W-2.
What to do about it: A settlement that mixes back pay and damages can change the tax line. Ask for the allocation in writing before signing.
Plain-language description of US practice, not legal, tax, or financial advice. The paired guide carries the citations, dates, and thresholds; the state pages carry the local windows.