Taken from Wikipedia OPC.
In short this industry standard allows intercommunication between devices and controllers Indistriales protocols almost all brands, performed monitoring and control from HMI, SCADA, PLC and RTU PAC'S
The OPC servers contain the drivers and / or communication protocols of the vast majority of industrial controllers
The OPC clients can be created in a variety of programming languages for reading and / or writing data to the server and there to the industrial controllers.
Examples of Architecture OPC (PLC Sensors Actuators - OPC Server and Client OPC)