ERP is a combination of "Planning" and "Resource".
Planning is the process of thinking about the activities required to achieve a desired goal. It is the first and foremost activity to achieve desired results. It involves the creation and maintenance of a plan, such as psychological aspects that require conceptual skills.
Resource: human, asset, equipment, customer, vendor, product, brand,...
So, ERP (or enterprise resource planning software) is an integrated system used by businesses to combine, organize and maintain the data necessary for operations. ERP systems merge each of the company’s key operations, including the manufacturing, distribution, financial, human resources and customer relations departments, into one software system. For many companies, the ERP software is the heart of their operations and the backbone of the organization.
In short, "ERP is a tool to help enterprise cut their operating costs".