In shortSCADA (Supervisory Control and Data Acquisition) is a system that collects data from field PLCs and devices and gives operators monitoring, alarms, trends and supervisory control.
SCADA sits above the control layer (PLCs) and below operations management (MES). It typically includes operator screens (HMI), alarm management, trend charts and often a data history (historian).
SCADA is built for real-time process visibility; carrying production confirmations to business systems such as ERP, or merging several sources into one data model, is not its main job. A separate integration layer is used for that kind of data movement.
For the difference between layers see the SCADA, MES and ERP article.
In OPC Router projects
OPC Router does not replace SCADA; it configures data exchange between SCADA, PLCs, databases and ERP systems.