Medicine Buddha is a fully enlightened being. To understand who he is, what his nature is, what his function is, and so on, we first need to understand what an enlightened being is. Generally, 'being' means any being who experiences feelings – pleasant, unpleasant, or neutral. Thus we are beings, and animals are beings; but houses and plants are not beings because they do not experience any feelings. There are two types of being: sentient beings and enlightened beings. A sentient being, or living being, is a being whose mind is afflicted by the darkness of ignorance. An enlightened being is a being who is completely free from the darkness of ignorance.