Pramāṇa (Sanskrit: प्रमाण, ) literally means "proof" and "means of knowledge". It refers to epistemology in Indian philosophies, and is one of the key, much debated fields of study in Hinduism, Buddhism and Jainism, since ancient times. It is a theory of knowledge, and encompasses one or more reliable and valid means by which human beings gain accurate, true knowledge. The focus of Pramana is how correct knowledge can be acquired, how one knows, how one doesn't, and to what extent knowledge pertinent about someone or something can be acquired.