What is meant by "extensions" to the ERP system which need to be implemented?

Enterprise resource planning (ERP) is a method of using computer technology to link various functions—such as accounting, inventory control, and human resources—across an entire company. ERP is intended to facilitate information sharing, business planning, and decision making on an enterprise-wide basis. ERP enjoyed a great deal of popularity among large manufacturers in the mid-to late-1990s. Most early ERP systems consisted of mainframe computers and software programs that integrated the various smaller systems used in different parts of a company. Since the early ERP systems could cost up to $2 million and take as long as four years to implement, the main market for the systems was