Satan refers to fallen angels (also known as the devil) recorded in the Bible. He is fallen angels who rebelled against God and was once an angel before the throne of God.
The original meaning of Hebrew is "opponent". Satan was once one of the highest angels in the sky, and Seraphim was before his fall. Because of his position, power and glory, he became confused and humble, and wanted to be equal to his creator Jehovah, so he was expelled from heaven by Jehovah.