Special use domains
I knew that
example.com was reserved as a domain for use in examples, but today I learned that
.test are reserved special-case TLDs
.example, .invalid, .local, .localhost, .onion, and .test are all "special use" domains.
"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."
via this news.yc comment
I had been using
.local for domains served on my computer already, I guess I didn't previously consider that it was something other than a convention.