Sindarin is the Elvish language most associated with the Elves of Beleriand in J.R.R. Tolkien’s legendarium.
Tolkien developed Sindarin as one of the major languages of his mythology. In the histories of Middle-earth, it was primarily spoken by the Sindar, or Grey Elves, who lived in Beleriand during the First Age. Its sound patterns were inspired especially by Welsh, one of Tolkien’s favorite languages.
Quenya is the other major Elvish language and is associated particularly with the High Elves and the Valinorean tradition. Tolkien designed relationships between these languages much as a historical linguist might reconstruct changes among related real-world languages.
Sindarin names appear throughout The Lord of the Rings, including Galadriel, Celeborn and Rivendell’s Elvish name, Imladris. The language is fictional, but Tolkien created substantial vocabulary and grammar rather than merely inventing isolated decorative words.