Special use domains

I knew that example.com was reserved as a domain for use in examples, but today I learned that .example, .invalid, .local, .localhost, .onion, and .test are reserved special-case TLDs

.example, .invalid, .local, .localhost, .onion, and .test are all "special use" domains.

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."

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.