When the owner of a domain name does not renew their ownership with their registrar, the latter deletes the domain name after its anniversary date.
From then on, the domain enters a period known as a "period of redemption". This is the safety period during which suppression is still reversible. During this phase, the domain name is no longer accessible but it still belongs to its former owner, who can request its restoration from their registrar until the last minute...
Redemption periods are different depending on the domain name's extension (TLD), and therefore on their registrars. For instance, .com domains have a redemption period of 30 days.
When this period ends, the domain name is definitively deleted and is made available for reservation.