Esperanta refers to certain universal ideas and concepts common to all intelligent life and has been called an "interplanetary" language. It is the principle upon which the universal translator is based. The translator compares the frequencies of brain wave patterns, selects those ideas it recognizes, and provides the necessary grammar. The device speaks with a voice, or the approximation of one, that corresponds to the identity concepts it recognizes.
The term was mentioned in several encounters in which the Enterprise crew were able to communicate with alien races, e.g. the natives of the planet Zarta, the Unoites and the natives of Trann. (TOS comics: "Invasion of the City Builders", "The Ghost Planet", "The Youth Trap") It was only later revealed (TOS episode: "Metamorphosis") that an electronic device, the universal translator, plays a role in such encounters.
- Esperanta is a nod to the international language of Esperanto.