Manvantara is a cyclic age (also spelled Manwantara; a.k.a. reign or age of Manu) in Hindu cosmology. At the beginning of a Kalpa (day of Brahma), Brahma creates Manu, the progenitor of mankind. In a Kalpa, there are 14 Manus who reign in succession, each ruling over a Manvantara, with the present being Vaivasvata Manu (7th).
Each Manvantaras repeats 71 Chatur Yugas (world ages), lasting for 306,720,000 years. In a Kalpa, which lasts for 1,000 Chatur Yugas (4.32 billion years), each of the 14 Manvantaras are followed by a Sandhya and the first Manvantara preceded by a Sandhya, with each Sandhya (connecting period) lasting the duration of a Satya Yuga (1,728,000 years). During each Manvantara-Sandhya, the earth (bhu-loka) is submerged in water.
In a Kalpa, there are 14 Indras who reign in succession in 14 Manvantaras.
Manvantara (Sanskrit: मन्वन्तर, lit. 'period or age of a manu') is a compound of "manu" (Sanskrit: मनु, lit. 'man') and "antara" (Sanskrit: अन्तर, lit. 'period'), i.e. "manu-antara" or "manvantara", literally meaning the duration of a Manu, or his life span.
(67) A year is a day and a night of the gods; their division is (as follows): the half year during which the sun progresses to the north will be the day, that during which it goes southwards the night. (71) These twelve thousand (years) which thus have been just mentioned as the total of four (human) ages, are called one age of the gods. (72) But know that the sum of one thousand ages of the gods (makes) one day of Brahma, and that his night has the same length. (79) The before-mentioned age of the gods, (or) twelve thousand (of their years), being multiplied by seventy-one, (constitutes what) is here named the period of a Manu (Manvantara). (80) The Manvantaras, the creations and descructions (of the world, are) numberless; sporting, as it were, Brahma repeats this again and again.
Twelve thousand divine years, each composed of (three hundred and sixty) such days, constitute the period of the four Yugas, or ages. ... a thousand such aggregates are a day of Brahma, and fourteen Manus reign within that term. Hear the division of time which they measure. Seven Rishis, certain (secondary) divinities, Indra, Manu, and the kings his sons, are created and perish at one period; and the interval, called a Manwantara, is equal to seventy-one times the number of years contained in the four Yugas, with some additional years: this is the duration of the Manu, the (attendant) divinities, and the rest, which is equal to 852,000 divine years, or to 306,720,000 years of mortals, independent of the additional period. Fourteen times this period constitutes a Brahma day, that is, a day of Brahma; the term (Brahma) being the derivative form.
In a Manvantara, fourteen Indras (sakras) reign in succession: