MDM and Netweaver
SAP NetWeaver is an integration and application platform that helps unify and align, information and business processes across technologies and organizations.
SAP Master Data Management (MDM) is a building block of SAP NetWeaver to enable information integrity across the business network and to facilitate a better communication of information across multiple systems.
Does MDM replace the existing master data distribution techniques for example between mySAP CRM and SAP ERP or SAP ERP and mySAP SCM? Read more 
Introduction to MDM
MDM is SAP Master Data Management. MDM enables data integrity across a multiple system, IT landscape. Now your SAP Master data, for example, business partners, product masters, product structures may be shared.
SAP MDM enables the sharing of harmonized master data, formerly trapped in multiple systems, and ensures cross system data consistency – regardless of physical system location. It helps to align master data by providing services that recognize identical master data objects and keep them consistent.
