.onion

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
onion
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
Used to access devices over the Tor network.

For further information, see The ".onion" Special-Use Domain Name (RFC 7686).