The Eldarin Languages
Elvish is a general term for the languages of the Elves. In Middle-earth, it most commonly refers to Sindarin, but can also apply to Quenya, the High-elven tongue. Other Elvish languages in Middle-earth include dialects derived from Sindarin (for example, the language of the Wood-elves of Thranduil). Eldarin is a term used to describe any of the languages of the Eldar, and especially Quenya and Sindarin, but excludes the tongues of the Avari.
Tolkein developed several Eldarin languages, but the ones we most hear about are Quenya and Sindarin. Quenya was also called High-Elvish and during the Third Age was not commonly spoken. It was used for ceremony, a sort of Elven Latin. Sindarin was spoken commonly by Elves in Middle-Earth during the Third Age. There exist other Elvish languages such as Telerin (spoken by the Sea-Elves of Tol-Eressëa) and Nandorin (also called Silvan)
The tongue of the High Elves in Valinor, the first to be recorded in writing. It was never widely used in Middle-earth except among the Noldor; the related Eldarin language, Sindarin, was more commonly spoken.
By the Third Age, Quenya had become, in Middle-earth, a language used only on formal or state occasions by the Elves and the descendants of the Númenóreans.
Quenya was also called High-Elven or Valinorian and the word "Quenya" means speach.
The language of the Grey-elves of Beleriand and most commonly used of the Elf-tongues in Middle-earth. When the Noldor returned to Middle-earth at the beginning of the First Age, Thingol decreed that their tongue, Quenya, was not to be spoken in his realms. So the language of his people, Sindarin, came to dominate. Quenya, though, was still used as a language of ceremony and poetry.
Sindarin shared common roots with Quenya, and the two languages had many similar words. Sindarin was said to be more changeful than the older tongue, however, and there were a number of regional 'dialects' of the tongue. The Sindarin spoken in Doriath was said to be the highest and most noble form of the language.
Sindarin was also called Grey-Elven and the word "Sindarin" means (Language) of the Grey People.