Bodhisattva Sanskrit; Pali, bodhisatta, “Enlightenment-Being”; Chinese, P-u-sa; Japanese, Bosatsu; Korean, Posal; Tibetan, byang.chub sems.dpa, “Hero of the Thought of Enlightenment”. It’s meaning is anyone with great compassion that has generated Bodhicitta.
In ancient indian buddhism, the word referred to Gautama Buddha.
In Theravada Buddhism this is a title exclusively identifying historical Buddhas, such as Sakyamuni, in their previous lives before attaining Buddhahood. In Mahayana Buddhism this is to describe any being who, out of compassion, has taken the Bodhisattva vow to become a Buddha for the sake of all sentient beings.
The Theravada concepts holds that there is only one Buddha, for this world cycle, and the the highest an ordinary man can aspire to be is that of an arhat or pratyekabuddha; while the Mahayana concept involves the belief the attainment of Buddha by Bodhisattva is possible for everyone.
Within the Mahayana, different levels or bhumi, as opposed to different types, of Bodhisattva are understood. Strictly, an ordinary person who has “engendered bodhicitta” generated a desire to save all beings from suffering, and taken the Bodhisattva vow is a Bodhisattva, but there are also “celestial Bodhisattvas,” such as Manjusri and Avalokitesvara, who are almost Buddhas in their attainments. Connecting these extremes is a series of bhumis, or stages, of a Bodhisattva’s development. These are standardized as ten by Dasabhumika-sutra, “Sutra on the Ten Stages,” which describes in detail the transformation in the bodhisattva’s understanding as he progresses toward Buddhahood.
In chinese buddhism, there are four great Bodhisattvas which are: Avalokitesvara (compassion), Manjusri (Wisdom), Kstigarbha (Vow) and Samantabhadra(Practice).
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, p. 155