Oportunity cost may defined as best altenative foregone which is also known as economic oportunity loss
Opportunity Cost is also known as Economic Opportunity Loss and it is the highest value alternative forgone. Moreover, Real cost is the fixed cost, which you have paid and therefore, opportunity cost is not a real cost. It cannot be considered as an explicit cost because in that case you actually make a payment. However, sometimes Economic Opportunity Loss involves a monitory payment and in that case, it is also an explicit cost. Otherwise, Opportunity cost is an implicit cost because an implicit cost is the forgone cost of an alternative action.
what is implicit cost