Samadhi is deep contemplation: mind and spirit brought to a close relationship. In much Indian speech it is treated as the peak of yoga or as a synonym for liberation.
Within the International Nath Order it is a station, not the last word. Meditation trains toward it. Mahendranath wrote that the Adinaths did not take samadhi as the end. Samarasa is the lasting equipoise that can follow, where microcosm and macrocosm are one. Awakening is the house name for that experiential union. Mahasamadhi is the passing of a yogi, not this sitting. None of these is a grade of initiation.