The apsarās are the celestial nymphs living in svargaloka (heaven). They perhaps got this name since they are supposed to move among waters, among the clouds. Their main work is to please Indra the lord of the gods, by dancing and singing. Indra often deputes them to seduce the sages engaged in severe austerities, since they may become more powerful than himself, if they succeed!
They are said to have been born out of the milk-ocean when it was churned by the gods and the demons to get nectar. According to other versions they were born out of the palm of Brahmā, the creator.
They are too numerous to be listed. Ūrvaśī, Raṁbhā, Menakā and Tilottamā are the most prominent among them.
They are closely associated with the demigods known as ‘gandharvas.’
Popular Buddhism has adopted some of them, in its mythological lore.