Kalpa (aeon)

A kalpa is a long period of time (aeon) in Hindu and Buddhist cosmology, generally between the creation and recreation of a world or universe.
Etymology.
Kalpa (), sometimes spelled calpa in British English, in this context, means "a long period of time (aeon) related to the lifetime of the universe (creation)", where its archaic spelling is kalp, with other forms of kalpam, ', and kalpe, derived from klip""' ().
Hinduism.
In Hinduism, a "kalpa" is equal to 4.32 billion years, a "day of Brahma" or one thousand "mahayugas", measuring the duration of the world. Each "kalpa" is divided into 14 "manvantara" periods, each lasting 71 "Yuga Cycles" (306,720,000 years). Preceding the first and following each "manvantara" period is a juncture ("sandhya") equal to the length of a "Satya Yuga" (1,728,000 years). A "kalpa" is followed by a "pralaya" (dissolution) of equal length, which together constitute a day and night of Brahma. A month of Brahma contains thirty such days (including nights), or 259.2 billion years. According to the "Mahabharata", 12 months of Brahma (=360 days) constitute his year, and 100 such years his life called a "maha-kalpa" (311.04 trillion years or 36,000 "kalpa" + 36,000 "pralaya"). Fifty years of Brahma are supposed to have elapsed, and we are now in the "Shveta-Varaha Kalpa" or the first day of his fifty-first year. At the end of a "kalpa", the world is annihilated by fire.
The definition of a "kalpa" equaling 4.32 billion years is found in the Puranas—specifically "Vishnu Purana" and "Bhagavata Purana".
The "Matsya Purana" (290.3-12) lists the names of 30 "kalpas", as follows:
The "Vayu Purana", in chapter 21, gives yet another list of 28 "kalpas", with five more in the next chapter.
Buddhism.
In the Pali language of early Buddhism, the word "kalpa" takes the form "kappa", and is mentioned in the assumed oldest scripture of Buddhism, the Sutta Nipata. This speaks of "Kappâtita: one who has gone beyond time, an Arahant". This part of the Buddhist manuscripts dates back to the middle part of the last millennium BCE.
Gautama Buddha claimed an incalculable number of Buddhas lived in previous "kalpas": Vipassi Buddha 91 "kalpas" ago, Sikhi Buddha 31 "kalpas" ago, and three prior Buddhas in the present "kalpa". He confines his teachings to the present "kalpa", the duration of which he doesn't arithmetically define, but uses a similitude:
Described in the Vibhanga division of the Abhidhamma Pitaka are sixteen "rupa brahma lokas" (worlds or planes) and four higher "arupa brahma lokas", each attained through the imperfect, medial or perfect performance of the four states of "jhana" (meditation), granting a duration of life measured in "kalpas" that exceed the top-most heavenly "loka" of 9.216 billion years:
At the termination of each "kalpa", the lower three "rupa brahma lokas", attained through the 1st "jhana", and everything below them (six heavens, Earth, etc.) are destroyed by fire (seven suns), only to later again come into being.
In one explanation, there are four different lengths of kalpas. A regular kalpa is approximately 16 million years long (16,798,000 years), and a "small" kalpa is 1000 regular kalpas, or about 16.8 billion years. Further, a "medium" kalpa is roughly 336 billion years, the equivalent of 20 small kalpas. A "great" kalpa is 4 medium kalpas, or around 1.344 trillion years.
The Buddha did not give the exact length of the "maha-kalpa" in terms of years. However, he gave several astounding analogies to understand it.
In one instance, when some monks wanted to know how many kalpas had elapsed so far, Buddha gave the below analogy:
Another definition of Kalpa is the world where Buddhas are born. There are generally 2 types of kalpa, "Suñña-Kalpa" and "Asuñña-kalpa". The "Suñña-Kalpa" is the world where no Buddha is born. "Asuñña-Kalpa" is the world where at least one Buddha is born. There are 5 types of "Asuñña-Kalpa":
The previous "kalpa" was the "Vyuhakalpa" (Glorious aeon), the present kalpa is called the "Bhadrakalpa" (Auspicious aeon), and the next kalpa will be the "Nakshatrakalpa" (Constellation aeon).
Popular culture.
"The Elder Scrolls" series.
The concept of kalpas was an inspiration for the kalpas of the universe of the "Elder Scrolls" series of action role-playing open world fantasy video games. In "The Elder Scrolls", kalpas represent each life cycle of the mortal realm of Mundus.
"City at the End of Time".
In "City at the End of Time", a science fiction novel by Greg Bear, Kalpa is a fortress city built on Earth by descendants of humans in the last period of the Universe to protect themselves from the Chaos that is devouring it.