Advanced Process Control (APC) is the technology for the (petro)chemical industries that makes it possible to control multivariable control problems. Since these controllers contain the dynamic relationships between variables it can predict in the future how variables will behave. Based on these predictitions, actions can be taken now to maintain variables within their limits.
Normally an APC system is connected to a Distributed Control System (DCS). The APC application will calculate moves that are send to regulatory controllers. Historicly the interfaces between DCS and APC systems were dedicated software interfaces. Nowadays the communication protocol between these system is managed via the industry standard OLE for process control (OPC) protocol.
Terminology: Manipulated Variables (MVs) are variables where advanced controllers send setpoints to. Controlled Variables (CVs) are variables that normally need to be controlled between limits. Disturbance Variables (DVs) are only used as an input to the controller, they cannot be influenced, but when measured contribute to the predictability of the CV.