Devas are celestial beings who reside in the 26 planes of existence above the human realm. They live far longer lives than humans and remain in a permanent state of bliss with no suffering nor worry. This realm signifies a higher spiritual existence marked by happiness and merit, and one can be reborn as a deva due to the karmic merits accumulated over their lifetimes.
The devas fall into three classes depending upon which of the three dhātus, or "realms" of the universe they are born in.
The devas of the top 4 planes of existence, the immaterial world, have no physical form or location, and they dwell in meditation on formless subjects. One can be reborn here by attaining advanced meditation levels in another life. They do not interact with the rest of the universe.
The devas of the fine-material world have physical forms but are genderless and passionless. They live in the 16 "heavens" or deva-worlds that rise, layer on layer, above the earth. The cause of being reborn in one of these heavens is the favourable karma accumulated through the practice of one of the dhyanas, meditation to reach a higher state of mind one step shy of enlightenment.
The devas of the sensuous world are the closest amongst the devas to humans. These devas are seduced by the pleasures of carefree indulgence in sensual enjoyment and fail to see their lives trickling away. However, when the time comes for them to die, they lose their beautiful complexions, their seats no longer feel comfortable, their flower garlands grow old, stains appear on their clothes, and perspiration, formerly absent, breaks out on their bodies.
The anguish they go through in dying is enormous and long lasting. Despite their attachment to the splendor and pleasure of their celestial state, they know they cannot help but be separated from them. They also know that once they have died, it is all but impossible to be reborn in the celestial realms again, and that even if a few of them are reborn as human beings, the majority will be reborn in the lower realms and will have to experience terrible suffering there for long periods of time. Rebirth here is determined by one's moral conduct (good or bad karma) and attachment to sensual pleasures.