The document discusses the modules that make up an Enterprise Resource Planning (ERP) system. It describes the main ERP modules as production planning, purchasing, inventory control, sales, marketing, finance, and human resources. Each ERP module mimics a major functional area of an organization and aims to consolidate departments and functions into a single system. The document provides details on the purpose and functions of the main production planning, purchasing, inventory control, sales, finance, and human resources modules.