"Bodhisattva (Skt; Pali, Bodhisatta). The embodiement of the spiritual ideal of Mahayana Buddhism, in contrast to the earlier Arhat ideal advocated in the Hinayana. Bodhisattva literally means 'enlightened being' but the correct Sanskrit derivation may be 'bodhi-sakta' meaning 'a being who is oriented towards enlightenment'. The ideal is inspired by the lengthy career of the Buddha before he became enlightened, as described in the Jatakas. A Bodhisattva begins his career by generating the aspiration (prajnidhana) to achieve enlightenment for the sake of all beings, often in the form of a vow, which according to many Mahayana texts is often accompanied by a prediction of success (vya-karana) by a Buddha. He then embarks on the path leading to enlightenment (bodhi) by cultivating the Six Perfections (sad-paramita) and the four means of attracting beings (sam-graha-vastu) over the course of three immeasurable kalpas. The spiritual progress of a Bodhisattva is usually subdivided into ten stages or levels (bhumi). Many Mahayana sutras state that a Boddisattva foregoes his own final enlightenment until all other beings in samsara have been liberated, or else describe a special form of nirvana, the unlocalized nirvana (apratistha-nirvana) by virtue of which a Bodhisattva may be 'in the world but not of it'. Earlier Mahayana sutras are specific in their belief that a Bodhisattva can only be male but later texts allow the possibily of female bodhisattvas."
-- Damien Keown --
("Oxford Dictionary of Buddhism")
Below, Lama Surya Das reads the Bodhisattva's vow from his book: "The Mind Is Mightier Than the Sword".