A cycle that describes the end of the world and the inevitable fall of civilization by subverting the people into pure materialistic beliefs, general evil and the subversion of degeneracy. Morality weakens and the people are the furthest from god and divine presence. Each cycle removes 1 leg of the bull of dharma meaning that 1 leg = 1 quarter of morallity. Golden age has the bull with four legs, kali yuga has just 1 leg present. We live in the kali yuga cycle, it started when Kalki left the earth to return to Vaikhunta.
Its the last of the 4 cycles. Kali yuga started on 18th February 3102 BCE