SAP MM (Materials Management) is a module in SAP ERP that handles procurement, inventory management, and invoice verification. It streamlines procurement and sourcing processes, provides real-time visibility of inventory levels, and allows for accurate invoice matching. Implementing SAP MM can reduce costs, automate workflows, and provide improved data and decision making through its integration with other SAP modules and real-time data exchange. Proper implementation requires planning, system configuration, testing, and ongoing user training and monitoring for best results.