Which Elvish writing system did J.R.R. Tolkien call the Tengwar?

J.R.R. Tolkien's Tengwar are also called the Fëanorian letters.

Tolkien designed the Tengwar as a writing system used for several languages in his legendarium. Their name comes from Quenya and means “letters” or “ 문자” in the relevant linguistic sense. The system is attributed in the fictional history to Fëanor, the great Noldorin Elf.

Tengwar appears in many famous inscriptions, including the text on the One Ring. Its elegant forms have also made it one of the most recognizable visual elements associated with Tolkien's languages and scripts.

Tengwar is not itself an Elvish language. It is a script that can represent different languages, much as one alphabet can be used for multiple real-world languages. Cirth is a separate runic script associated especially with Dwarves and other peoples.