Sindarin is the Tolkien language primarily associated with the Sindar, or Grey-elves, of Middle-earth.
In Tolkien’s mythology, Sindarin developed from the speech of Elves who remained in Middle-earth rather than completing the journey to Valinor. It became a major living language among Elves in the later history of the fictional world. Names such as Mithrandir, Galadriel, and Minas Tirith contain Sindarin elements.
Tolkien based much of Sindarin’s sound and structure on Welsh, while Quenya was strongly influenced by Finnish and Latin. These influences are useful clues, but the languages are Tolkien’s own constructed systems rather than simple copies of real languages.
Sindarin and Quenya are often confused because both are Elvish languages and both appear in The Lord of the Rings. Quenya is associated especially with the High Elves and has a more formal or ceremonial role in much of the Third Age. Sindarin is the more commonly spoken Elvish language in that setting.