The great bird of the galaxy was a mythological creature evoked as a blessing.
Background information Edit
The Great Bird of the Galaxy was the nickname of Star Trek creator Gene Roddenberry, given to him by Associate Producer Robert Justman. (Star Trek Encyclopedia (4th ed., vol. 1, p. 317)) In a memo Roddenberry wrote Justman about some of the final script revisions to TOS: "What Are Little Girls Made Of?" (the memo was dated 28 July 1966), Roddenberry joked, "May the great bird of the galaxy never fly over your pool table."
An early Okudagram was later created during TNG Season 1 that depicted an image of the great bird – Gene's face placed on the body of a parrot wearing a Starfleet uniform. It is seen briefly in TNG: "The Naked Now" at 15:00. The Okudagram was based on a full-color painting Andrew Probert made, as a gift for Roddenberry's sixty-sixth birthday, in 1987. (Star Trek: The Next Generation 365, pp. 130-131)