Answer:
Resources are not effectively utilised
Step-by-step explanation:
Production possibility frontier (PPF) represents the resources a society can use. If the resources are utilised effectively the economy will operate outside the frontiers. Similarly, if the economy is not utilising the resources efficiently the economy will operate under frontier. This generally happens in recession and depression. In the state of recession and depression, society is unable to use all the resources which lead to low production and output.