Hindu philosophy refers to a group of darśanas (philosophies, world views, teachings) that emerged in ancient India. The mainstream Hindu philosophy includes six systems (ṣaḍdarśana) – Samkhya, Yoga, Nyaya, Vaisheshika, Mimamsa and Vedanta. These are also called the Astika (orthodox) philosophical traditions and are those that accept the Vedas as authoritative, important source of knowledge.[note 1][note 2] Ancient and medieval India was also the source of philosophies that share philosophical concepts but rejected the Vedas, and these have been called nāstika (heterodox or non-orthodox) Indian philosophies. Nāstika Indian philosophies include Buddhism, Jainism, Cārvāka, Ājīvika, and others.