Sindarin is the language associated with the Grey-elves of Middle-earth in J.R.R. Tolkien’s fiction.
Tolkien developed Sindarin as one of the major Elvish languages in his legendarium. It is based partly on the sound patterns and historical relationships of Welsh, one of the real languages that influenced his linguistic imagination.
Sindarin is linked especially with the Sindar, or Grey-elves, who lived in Beleriand during the First Age. In the later history of Middle-earth, it became a widely used Elvish language in many regions, including among characters such as Legolas and Elrond’s household.
Quenya is the other major Elvish language and is associated more strongly with the High Elves. The two are related within Tolkien’s fictional language history, but they are not interchangeable names.