ERP is the abbreviation for Enterprise Resource Planning. It is a type of business software that organizations use that is part of a system of integrated applications. The largest providers of ERP software are SAP, Oracle and Microsoft. Other players include:

Lawson - in the enterprise, on-premise ERP and CRM software market
Infor - in the enterprise, on-premise ERP and CRM software market
NetSuite - in the SaaS ERP software market
Sage - in the SMB on-premise accounting software, CRM and ERP software market