In the Marvel Comics universe, Galactus is not considered a Celestial, but rather a cosmic entity of immense power and hunger. He is often referred to as the Devourer of Worlds, as he consumes the energy and matter of entire planets in order to sustain his own existence.
The Celestials, on the other hand, are a group of fictional characters who are ancient and powerful beings that possess god-like powers and have played a key role in shaping the Marvel Universe. They are often depicted as towering, armored figures with a range of abilities, such as the ability to manipulate matter and energy, fly, and teleport.
While Galactus is not a Celestial, he does have a connection to them in the Marvel Comics mythology. According to some storylines, Galactus was created by the cosmic entity known as the Big Bang, which was itself created by the Celestials as part of their experiments in creating new universes.