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. 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.