Short answers, pulled from the story.
Bodhisattva combines bodhi, meaning awakening or enlightenment, and sattva, a term with disputed meaning. Scholars have translated it as sentient being, heroic being, spiritual warrior, one devoted to bodhi, and one capable of enlightenment. Tibetan lexicographers combined two readings, rendering it as sems dpa, which joins mind and hero.
In Theravada Buddhism, a bodhisattva is an exceptionally rare individual who has made a resolution in front of a living Buddha and received that Buddha's personal prediction of future Buddhahood. In Mahayana Buddhism, anyone who generates bodhicitta, a compassionate wish to attain Buddhahood for the benefit of all beings, is considered a bodhisattva, and the path is open to everyone.
Bodhicitta is a spontaneous, compassionate wish and mind directed toward attaining Buddhahood for the benefit of all sentient beings. In Mahayana Buddhism, the arising of bodhicitta is the first step in the bodhisattva career, as described in the Ten Stages Sutra. According to Atiśa's 11th-century Bodhipathapradīpa, it is the central defining feature of a Mahayana bodhisattva.
Most Buddhist sources describe the path as extraordinarily long. The Mahāyānasaṃgraha of Asanga states the bodhisattva must cultivate the six perfections for three incalculable aeons. Shantideva wrote that each perfection requires sixty aeons of practice. Some sutras estimate the full path could take anywhere from three to twenty-two countless aeons, amounting to many billions of years.
The most important bodhisattvas in Mahayana Buddhism are Avalokiteshvara, the bodhisattva of compassion; Mañjuśrī, the bodhisattva of wisdom; and Maitreya, the future Buddha. In the Eight Great Bodhisattvas tradition, Vajrapāṇi, Kṣitigarbha, Ākāśagarbha, Sarvanivāraṇaviṣkambhin, and Samantabhadra are also included. Guanyin, the female form of Avalokiteshvara, is the most widely revered bodhisattva in East Asian Buddhism.
The ten bhūmis, or stages, are listed in the Daśabhūmikasūtra. They run from Great Joy, where generosity is emphasized, through Stainless, Luminous, Radiant, Very Difficult to Train, Obviously Transcendent, Gone Afar, Immovable, Good Discriminating Wisdom, and finally Cloud of Dharma, after which full Buddhahood is attained. A bodhisattva above the seventh stage is called a mahāsattva.