Bodhisattva - A Bodhisattva is basically a Buddha in the Mahayana school of Buddhism. A Bodhisattva is one who is enlightened and one who truly seeks to guide others to enlightenment out of pure compassion. The Bodhisattva ideal incorporates both wisdom and compassion. As opposed to the Theravada school of Buddhism, where there was only one Bodhisattva (the Buddha), the Mahayana school thought that everybody could become a Bodhisattva. What makes a person a Bodhisattva, as opposed to being called a Buddha, is that the enlightened individual chooses to return to the cycle of samsara and help others attain enlightenment. A very popular Bodhisattva was Avalokitesvara, whose name actually means "he who watches with compassion", which is one of the main ideas of being a Bodhisattva.
Karma - Karma is basically the old saying "what comes around goes around". Karma can be looked upon as the product of moral or immoral action and it is the principle of moral causation in Buddhist thought. An example of karma would be: For every event that occurs, there will follow another event whose existence was caused by the first, and this second event will be pleasant or unpleasant according as its cause. One the most significant ideals taught in Buddhism was that of morality, which in turn led to a huge belief in karma. This was because the idea of destiny and the fact that what one did in the present controlled the future rang true to many Buddhists. Another reason as to why karma was so widely accepted was because it spoke almost directly to the attaining of enlightenment. It seemed to say act accordingly now and you will be rewarded with nirvana after proceeding along the right path, a very simple cause and effect.
Nirvana - Nirvana is the main goal of Buddhism. Nirvana is the supreme level of consciousness, at which one is completely in tune with one's surroundings. Once reaching nirvana the cycle of samsara is broken one must no longer endure the suffering of everyday life and rebirths.
