The coming into existence of another being based on conditions arising from a previous existence. This is commonly confused with reincarnation. Reincarnation is the passing of a soul or spirit into a new body. Buddhism denies the concept of a soul, spirit or permanent self therefore in Buddhism rebirth occurs but there is no-one who is reborn.
Rebirth in Buddhism is the doctrine that the evolving consciousness (Pali: samvattanika-viññana) or stream of consciousness (Pali: viññana-sotam, Sanskrit: vijñāna-srotām, vijñāna-santāna, or citta-santāna) upon death (or "the dissolution of the aggregates" (P. khandhas, S. skandhas)), becomes one of the contributing causes for the arising of a new aggregation. The consciousness in the new person is neither identical nor entirely different from that in the deceased but the two form a causal continuum or stream.
In traditional Buddhist cosmology these lives can be in any of a large number of states of being including the human, any kind of animal and several types of supernatural being. Rebirth is conditioned by the karmas (actions of body, speech and mind) of previous lives; good karmas will yield a happier rebirth, bad karmas will produce one which is more unhappy. The basic cause for this is the abiding of consciousness in ignorance (Pali: avijja, Sanskrit: avidya): when ignorance is uprooted, rebirth ceases. One of the analogies used to describe what happens then is that of a ray of light that never lands.