Impermanence is one of the key concepts of the Buddhist teaching (). It describes the basic nature of everything that has come into existence, namely transience.
«It is like milk, which when once taken from the cow, turns, after a lapse of time, first to curds, and then from curds to butter, and then from butter to ghee. Now would it be right to say that the milk was the same thing as the curds, or the butter, or the ghee?’ ‘Certainly not; but they are produced out of it.’ ‘Just so, O king, is the continuity of a person or thing maintained. One comes into being, another passes away; and the rebirth is, as it were, simultaneous. Thus neither as the same nor as another does a man go on to the last phase of his self-consciousness.»1
The Questions of King Milinda, II 2.2
1 The Questions of King Milinda, translated by T. W. Rhys Davids, Oxford University Press 1890, p. 65.