Dangling DNS Record
A DNS record pointing at a resource the owner no longer controls (an unclaimed CDN hostname, deleted cloud bucket, expired domain), the prerequisite for most subdomain takeovers.
A dangling DNS record is a CNAME, A, or NS that points at infrastructure the domain owner has already abandoned: a CNAME to an Azure App Service that was deleted, an A record to an EC2 IP that was released back to the pool, an NS pointing to a registrar that no longer hosts the zone. Whoever claims the target next inherits whatever was at that hostname, which is the mechanic behind subdomain takeover. Routine zone audits, low TTLs on temporary records, and removing DNS entries before tearing down the resource (not after) prevent most danglers.