J.R.R. Tolkien gave the language spoken by many Elves of Beleriand the name Sindarin.
Sindarin is one of Tolkien’s most developed Elvish languages. In the First Age, it is associated especially with the Sindar, or Grey Elves, who remain in Middle-earth rather than completing the journey to Valinor. Beleriand is the region where many of the language’s major First Age stories take place.
Tolkien based Sindarin’s sound and historical development partly on Welsh, while Quenya was influenced more strongly by Finnish and Latin. The two languages are related within Tolkien’s fictional history but are not interchangeable.
In The Lord of the Rings, Sindarin appears in names such as Galadriel, Celeborn, and Rivendell. Quenya remains a prestigious, older language, so readers sometimes identify every Elvish name as Quenya; Tolkien’s linguistic distinctions are more specific than that.