In 2365, the Federation starships USS Atlantis and NCC-21335 were on diplomatic missions to this planet. It was listed in the chart Starship Deploy Status, which was seen in the Starbase 173 courtroom. (TNG: "The Measure Of A Man", okudagram)
This planet was only mentioned in writing.
The reference to this planet, as well as the wording of several okudagrams, was an in-joke. Alderaan was the adopted homeworld of Star Wars' Princess Leia, who claimed to be on a diplomatic mission to Alderaan when captured by Darth Vader in the opening scene of Star Wars Episode IV: A New Hope.
The name of this planet originally also appeared in "Up The Long Ladder", on an okudagram on Picard's desktop monitor as the destination of HMS New Zealand in 2135. A legible version of the original okudagram appeared in the reference book, Star Trek: The Next Generation - The Continuing Mission. In the remastered version of the episode, the planet was renamed to Aldebaran.