The universe is a cyclic phenomenon that comes into existence and dissolves repeatedly.
Kalpa->Manvantara->yug cycle->yug ages
Each kalpa cycle is presided over by a number of Manus, one for each manvantara
each manvantara has a number of yuga cycles,
each with four yuga ages of declining virtues.
Kalpa->Manvantara->yug cycle->yug ages