https://en.wikipedia.org/wiki/List_of_Internet_top-level_dom...
"ICANN/IANA has created some Special-Use domain names which are meant for special technical purposes. ICANN/IANA owns all of the Special-Use domain names."
".test" is recommended for use in testing of current or new DNS related code.
".example" is recommended for use in documentation or as examples.
".invalid" is intended for use in online construction of domain that are sure to be invalid and which it is obvious at a are invalid.
The ".localhost" TLD has traditionally been statically defined in DNS implementations as having an A record pointing to the back IP address and is reserved for such use. Any other use conflict with widely deployed code which assumes this use.
[0] https://datatracker.ietf.org/doc/html/rfc2606 test
example
invalid
localhost
local
localdomain
domain
lan
home
host
corp
0. https://www.ietf.org/archive/id/draft-chapin-rfc2606bis-00.h...https://datatracker.ietf.org/doc/html/rfc2606#page-2 https://datatracker.ietf.org/doc/html/rfc6761
You are probably safe using names like .lan and .corp but they are not currently protected by standard in the way example is.