The Ramatis system was an inhabited planetary system in the Beta Quadrant. This system consisted of the primary Ramatis and at least three planets, including Ramatis III.

In 2257, during the first Federation-Klingon War, this system was occupied by the Klingons. (DIS: "The War Without, The War Within")

In the year 2365, the USS Enterprise-D was diverted to Ramatis III in order to transport Riva, a famous mediator, from his homeworld to Solais V where he would negotiate for an end to a centuries long planetary conflict. (TNG: "Loud As A Whisper"; DIS: "Magic to Make the Sanest Man Go Mad")

"RAH-mah-tis." was the pronunciation for this system's name from the script pronunciation guide. [1]
According to Star Trek: Star Charts (p. 61) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), the Ramatis system was a trinary system with a G-class star, a K-class star, and a M-class star.
Ramatis, the primary of the Ramatis system, was located in the Beta Quadrant on a star chart seen in the Star Trek: Discovery episode "Magic to Make the Sanest Man Go Mad".