SAP is an enterprise resource planning application product developed by German software company SAP AG. The current version of SAP is called SAP R3. SAP was launched in 1970's and subsequent versions of SAP were SAP R1, SAP R2, and now SAP R3.
SAP R3 has has a Technical module which deals with programming and development and Functional modules which are trade specific like finance, operations, HR, etc.
What SAP is can best be best understood by the benefits resulting when an enterprise implements it as an ERP solution. SAP R3 integrates all the branches of an enterprise and brings them under a single application thus improving interdepartent communication resulting in better decision making and advance planning as all the reports and data is becomes online, which is not possible in any other known platform.
SAP is a leader in ERP with more than 50% market share worldwide. SAP professionals are in high demand and are highly paid specially those who work on functional modules.