Lockdown 4.0: What are buffer, containment zones?

According to the MHA's latest order, states/UTs have now been given the power to decide on the delineation of red, green and orange zones. This is in accordance with suggestions by various chief ministers who had urged the PM to grant them the authority during the most recent virtual interaction held earlier this month. The Prime Minister had also said that states will be given more power to take control of the situation going ahead.