Off-label use means a licensed clinician prescribes an approved medicine for a condition, age group, or dosage form not listed in the FDA-approved labeling. It is legal, common, and sometimes supported by substantial published evidence.
What off-label means in practice is that the specific use has not gone through the FDA review process for that product, so the labeling contains no guidance on it. Asking a prescriber directly whether a use is on-label or off-label, and what evidence informs it, is a reasonable question.