Ritu (ṛtú) in Vedic Sanskrit refers to a fixed or appointed time, especially the proper time for sacrifice (yajna) or ritual in Vedic Religion, The word is so used in the Rigveda, the Yajurveda and the Atharvaveda. In Classical Sanskrit, it refers to an epoch or period, especially one of the six seasons or ritus in the Hindu calendar, Vasanta/Basant "spring", Grishma "the hot season", Varsha "the rainy season", Sharad "autumn", Hemant "winter"; and Shishir "the cool season", or the menstrual cycle.
It is also the name of a Rishi and of the 12th Manu.
Rtu in its diverse meanings can also be associated with food as is described in the Rig Veda. Hymn 15 Book 1.