Tengwar is the writing system J.R.R. Tolkien created for scripts used by many Elves.
The Tengwar, also called the Fëanorian characters, were devised within Tolkien’s fictional history by Fëanor. In the stories, the system was adapted for several languages and became widely used across Middle-earth, including for Quenya and Sindarin.
Tolkien designed Tengwar with careful attention to how sounds are represented. Its letters can be arranged in different modes, so the same general script may record different languages in different ways. This is why identifying the script alone does not always identify the language.
Tengwar is also used for the Ring-inscription, even though that inscription is in the Black Speech. Cirth is a separate runic writing system associated especially with Dwarves and northern peoples, making it the most common alternative answer to this question.