युग
Also known as Chatur-yuga (the cycle of four ages)
The yuga cycle is the measure of time named at SB 3.8.12 in 'chatur-yugAnAM cha sahasram apsu svapan' — the Lord sleeps in the waters for a thousand cycles of the four yugas. The roster holds kali-yuga and dvapara-yuga as separate entities; here the verse speaks of the cycle as a whole, so 'yuga' is declared as the aggregate measure of time. The mentions of the end of an age at SB 3.8.23, 'yugAnta-toye', and at SB 3.8.17, 'yugAnta-shvasanAvaghUrNa-jalormi-chakrAt', refer to the close of this same cycle.
Śrīmad Bhāgavata Mahāpurāṇa 3.8.12 — Sanskrit Wikisource (pinned chapter page; Devanagari from the cross-validated transcription in validation/sanskrit_skandha3.json)
At SB 3.8.12 the Lord is described as sleeping in the waters 'chatur-yugAnAM cha sahasram apsu svapan' — for a thousand cycles of the four yugas. The yuga cycle is therefore declared as an entity distinct from kali-yuga and dvapara-yuga, being the aggregate measure of time.
At SB 3.11.22 the day of Brahma is given as equal to a thousand ages of the three worlds, and the night as of the same length. At SB 3.11.20 the time between the junction and the portion is what is called an age, in which dharma is enjoined.
