Quenya is the Tolkien language spoken by the elves of Valinor in The Lord of the Rings appendices.
Tolkien developed Quenya as a major Elvish language, drawing especially on the sounds and structures of Finnish, Latin, and Greek. In his internal history, it was associated with the high elves, including the Noldor and Vanyar, and was spoken in Valinor before many Noldor returned to Middle-earth.
By the time of The Lord of the Rings, Quenya functioned largely as a learned, ceremonial, or literary language among many elves in Middle-earth. Sindarin was generally the more widely spoken Elvish language there. This distinction is why famous phrases such as “Namárië” and “Elen síla lúmenn’ omentielvo” are often identified with Quenya.
Quenya and Sindarin are sometimes treated as interchangeable because both are Elvish languages created by Tolkien. They have different histories, vocabulary, and grammatical development within his fictional world.