Ritu (Sanskrit: ऋतु) or Kaalanilai (Tamil: காலநிலை) means "season" in different ancient Indian calendars used in India, Bangladesh, Nepal and Sri Lanka. There are six ritus (also transliterated ritu) or seasons. The word is derived from the Vedic Sanskrit word Ṛtú, a fixed or appointed time, especially the proper time for sacrifice (yajna) or ritual in Vedic religion; this in turn comes from the word Ṛta (ऋत), as used in Vedic Sanskrit literally means the "order or course of things". This word is used in nearly all Indian languages.