What is the difference between maximum demand and overload in power system???

Maximum demand:
Maximum demandregister (kW or kVA). This is themaximum powervalue, usually the average of 15 minutes, reached during the billing period (this average time may vary depending on the country). Once the value is higher than the contractedpower, the customer will pay a penalty on the electricity bill.
It is the Greatest demand of load on the power station
during a given period. it sometimes also called as "system
peak" It is called maximum demand.

Overload:
Overloadand back-up for distance (overcurrent)Overloadprotection requires a current transformer which simply measures the current in a circuit. ... Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate.