Tengwar is the writing system Tolkien uses for many Elvish inscriptions in Middle-earth.
Tengwar means “letters” in Quenya. Tolkien designed the script as part of his invented history of languages and writing systems, and its letter shapes are associated especially with Fëanor. The script can represent several languages, including Quenya, Sindarin, and the Common Speech, depending on the mode used.
The inscription on the One Ring is written in Tengwar characters, although the language of the inscription is the Black Speech of Mordor. This distinction is important: a script is a writing system, while a language is the spoken or written tongue represented by it.
Tengwar is different from Cirth, the angular runic script associated particularly with Dwarves and carved inscriptions. Tolkien’s detailed appendices and illustrations helped make both systems recognizable to readers and later fans.