The description of the word you requested from the astronomical dictionary is given below.
The International Astronomical Union (IAU) is the official international organization for astronomy. Among other tasks, the IAU defines standards for use in astronomy. The IAU determines the official name of things in our Solar System outside the Earth, such as for moons, comets, and asteroids, and for craters and mountains on other planets, moons, and astroids. The IAU has also defined the boundaries and names of the official constellations. The web site of the IAU is at //www.iau.org.