A planet at the centre of an artificial system of eight suns, where an ancient warning about synthetic life, the Admonition, was left and later found by the Romulans.
Aia, called the grief world by the Romulans, lies in an octonary star system: eight suns held in an arrangement that could not be natural. Its builders set it up as a beacon to draw attention to the message stored on the planet.
That message, the Admonition, floods the mind with visions of destruction linked to the rise of synthetic life. The Romulans who found it centuries ago founded the Zhat Vash to stamp out such life wherever it appears. The Picard episode Broken Pieces shows a group of initiates led by Commodore Oh receiving it on Aia; most are driven to kill themselves, and Narissa and her aunt Ramdha are among the few who live.
In Et in Arcadia Ego the android Sutra experiences the same message and reads it as a promise of help addressed to synthetics.