Bhagavat-Gita (Sans.) Lit., "the Lord's Song," a portion of the Mahabharata, the great epic poem of India. It contains a dialogue wherein Krishna — the "Charioteer" and Arjuna his chela have a discussion upon the highest spiritual philosophy. The work is pre-eminently occult or esoteric.
Source: H.P.Blavatsky - The Key to Theosophy, The theosophical glossary