An unlisted number is a phone number that is not listed in a public directory. This means that it is not available to the general public and is not easily found. Full definition
4 -1-1 Charges Appealed, Unlisted Number Service, PIAC Commissions Special Study on Government's Plans to Auction Spectrum, Ontario Government White Paper Proposes Change, Amendments to the Telecommunications Act, New Reports (piac.ca)
On the caring list, PVS is now an unlisted number — not only in the dying context where nothing more reasonable can be done, but now in the chronic cases who are simply not dying fast enough. (firstthings.com)
The Oilers have an unlisted number for the other teams. (sbnation.com)