The Two Worlds was a term coined by Romulans and others in the Romulan Star Empire, used to refer to the capital planets of Romulus and Remus.
History and specifics[]
Donatra and Norvid used this term to refer to Romulus and Remus in conversations they had in the year 2380. (TNG novel: Q & A)
Another term used was Hearthworlds. (TOS - Rihannsu novels: Swordhunt, Honor Blade, The Empty Chair, TNG - Tales of the Dominion War short story: "The Ceremony of Innocence is Drowned")