ERP is a general term.Any integrated module is an ERP.The SAP is an large scale industry accepted standard ERP System.The SAP is available in different verticals like manufacturing SCM HRMS Finance etc

ERP is generally referred to a class of business softwares that addresses a business firm in totality rather than one or two functions.

For example there are accounting softwares inventory softwares etc. that addresses a specific function of a business. But an ERP class software adrresses all the functions of the business and provides an integrated view of the business to the management.

SAP is a German company and is the world leader in ERP softwares across various industries.

what is ERP and how it is related to SAP?

ERP is a technology to plan various resources according to the imporvement of the enterprise. SAP is a tool to implement the technology.