Sindarin is J.R.R. Tolkien’s invented Elvish language most associated with the Grey-elves of Middle-earth.
In Tolkien’s internal history, Sindarin developed from the language of the Teleri who remained in Middle-earth. The name refers to the Sindar, or Grey-elves, and the language is especially connected with Beleriand and later with the Elves of western Middle-earth.
Sindarin is one of Tolkien’s most fully developed invented languages. Its sound and structure were influenced strongly by Welsh, while its fictional history links it to other Elvish languages such as Quenya. In The Lord of the Rings, names including Galadriel, Celeborn, and Lothlórien reflect Tolkien’s Elvish linguistic construction.
A common mix-up is treating Sindarin and Quenya as interchangeable. Quenya is the more formal High-elven language, while Sindarin became the everyday Elvish language for many communities in Middle-earth during the later ages.