Domain ownership
Technically you don't 'own' a domain — you hold a renewable lease from the registry. The registration grants exclusive use for the term you've paid for, up to 10 years.
Practical effect
For day-to-day purposes, registrant = owner. You can transfer it, sell it, will it. But the underlying right is contractual — let the registration lapse and the name returns to the public pool.
Renewal hygiene
Auto-renew + a backup payment method saves more domains than any other single practice.