SCADA Server or Master Terminal Unit (MTU).
Other International Definitions
The SCADA Server is the device that acts as the master in a SCADA system. Remote terminal units and PLC devices (as described below) located at remote field sites usually act as slaves. 
- ↑ K. Stouffer, J. Falco, K. Kent, Guide to Industrial Control Systems (ICS) Security, NIST Special Publication 800-82, June 2011