Devas are heavenly deities in various Asian myths. In Vedic mythology, they were the gods of natural phenomenon, and constantly competed with the Asuras, who in this case were gods of moral/social phenomenon.
In Hinduism, Devas and Asuras were both demigods who are at constant war. In Buddhism, Devas were lesser deities who you could reincarnate into if you accumulated enough good karma. In Zoroastrianism, they were called Daevas and were evil, false deities who were to be rejected for being misled by "The Lie".