SCADA is an acronym to supervisory control and data acquisition.
It is a system that retrieves data from devices inside the factory in real-time.
The SCADA system stores this information and generate reports.
They can read and control variables from this devices through equipment like PLC (Programmable Logic Controller). The SCADA systems can also act like an HMI (check out these recommendations Human Machine Interface).
A little slide to help to understand the basics principles of SCADA: