en·tro·py /ˈentrəpē/ noun noun: entropy; plural noun: entropies; symbol: S

1. In physics a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.
"the second law of thermodynamics says that entropy always increases with time"
2. lack of order or predictability; gradual decline into disorder.
"a marketplace where entropy reigns supreme"

What happens at Max entropy? When the entropy reaches the maximum value, the heat death of the universe happens. Heat death happens when the universe has reached equilibrium due to maximum entropy. This will happen when all the energy from the hot source moves to the cold source and everything in the universe will be of the same temperature.