Impermanence
Anicca or impermanence is understood by Buddhists as one of the three marks of existence, the others being dukkha (unsatisfactoriness) and anatta (non-selfhood). All things in the universe are understood by Buddhists to be characterised by these three marks of existence. According to the impermanence doctrine, human life embodies this flux in the aging process, the cycle of birth and rebirth (samsara), and in any experience of loss. This is applicable to all beings and their environs including devas (mortal gods). The Buddha taught that because conditioned phenomena are impermanent, attachment to them becomes the cause for future suffering (dukkha).
Conditioned phenomena can also be referred to as compounded, constructed, or fabricated. This is in contrast to the unconditioned, uncompounded and unfabricated nirvana, the reality that knows no change, decay or death.
Impermanence is intimately associated with the doctrine of anatta, according to which things have no fixed nature, essence, or self. For example, in Mahayana Buddhism, because all phenomena are impermanent, and in a state of flux, they are understood to be empty of an intrinsic self (shunyata).
Read more about this topic: Annitya