OPC Server

An OPC Server is a software application that acts as an API (Application Programming Interface) or protocol converter. An OPC Server can connect to a device such as a PLC, DCS, and RTU or a data source such as a database or HMI to translate the data into a standard OPC format.

OPC

Open Process Connectivity (OPC) is a set of connectivity standards to provide a set of common interfaces for process control. OPC allows information exchange between gauges, databases, and programmable logic controllers (PLCs).

OPC-UA

OPC Unified Architecture (OPC-UA) is a communication protocol for interoperability developed by the OPC Foundation . The Foundation's goal for this project was to provide a path forward from the original OPC communications model (namely COM/DCOM) to a cross-platform service-oriented architecture (SOA) for process control, while enhancing security and providing an information model.

Using the OPC-UA module, Ignition acts as an OPC-UA server, serving data collected by its built in drivers to other Ignition modules, as well as third-party OPC-UA clients. -Wikipedia