An abandoned domain is a domain name that is no longer actively maintained or monitored. It may have expired, been deliberately retired, or simply been forgotten, even while older software or services still refer to it.
This matters because a lingering reference can leave a trust gap. If an attacker can register or take control of the domain, they may be able to redirect traffic or impersonate a service, depending on how the software uses it. Defenders should inventory domain dependencies, renew domains that must remain in use, and remove or update references that are no longer needed. These steps are especially important for legacy systems, which may continue relying on external names long after their original owners stop watching them.