SCADA is an acronym that stands for Supervisory Control and Data Acquisition.
At its essence SCADA means data is acquired and used to observe, evaluate and control things.
Because there are so many different ways to acquire data, observe, evaluate and control things there are practically unlimited different SCADA systems and applications possible.
SCADA systems are used to monitor and control manufacturing processes, activities, machines, buildings, security systems, software systems, the state of networked devices and many other things.
SCADA software exists to access data, store data, analyze data, automate actions and decisions based on data, notify people about data, and format and display data in useful ways to people.
Check out Ignition, a SCADA software product.