What do you mean by resource allocation and economic efficiency

Resource allocation: Allocation of resources is a central theme in economics which is essentially a study of how resources are allocated and is associated with economic efficiency and maximization of utility. 

Economic efficiency: Economic efficiency implies an economic state in which every resource is optimally allocated to serve each individual or entity in the best way while minimizing waste and inefficiency.

When an economy is economically efficient, any changes made to assist one entity would harm another.