Sindarin is the language J.R.R. Tolkien developed for the Grey-elves.
Sindarin is one of Tolkien’s major Elvish languages and is associated with the Sindar, or Grey-elves. In the linguistic history of Middle-earth, it developed from earlier forms of Elvish and was used widely among Elves in Beleriand and later among many Elves of Middle-earth.
Quenya is the other best-known Elvish language, but it is associated especially with the High Elves and has a more formal or ceremonial role in many settings. Tolkien constructed both languages with detailed sound systems, grammar, and historical relationships, drawing inspiration from languages such as Welsh and Finnish.
Names such as Lúthien, Galadriel, and Celeborn are connected with Tolkien’s Elvish linguistic work, although fictional names can have different historical forms. Sindarin is therefore not simply a generic word for every Elvish speech in the legendarium.