.localhost

String Information
A-label ASCII form of the domain name, which is used internally in the DNS to represent this domain using the IDNA protocol
localhost
Category Classification based on purpose and governing global allocation policy
Special-use top-level domain
Script The writing system (script) used for this domain label
Latin Latn
Status The current delegation status of the string
Reserved
Technical Status
Not delegated
Remarks
The .localhost domain is typically configured to point to your device, i.e. to IP address 127.0.0.1 (IPv4) or ::1 (IPv6). This is known as a loopback, and it is widely used in software development and testing when an application needs to connect to another service running on the same device.

For further information, see Special-Use Domain Names (RFC 6761) and Reserved Top Level DNS Names (RFC 2606).