ERP stands for Enterprise Resource Planning — a type system, that you might want to run a business – lots of companies sell ERP software.
SAP is a company which creates ERP software products. The main SAP product that is pretty much what everyone refers to when they are talking about SAP is a ERP system.
knowledge of ERP is useful,but SAP has its own set of configurations .
There are also some other ERP software like Oracle and many more.