It is an offer without the pre-authorisation of the holding deposit. If you accept an offer without deposit, the tenant will have 24 hours to pay the holding deposit. Without the deposit paid there isn't a guarantee that they will continue in the process.
Until then, the listing will stay on the market and open to other renters. You may receive and accept other offers during this time. If the tenant fails to pay within 24 hours, their offer will expire and your property will continue to stay on the market. Learn about offers with deposits