Traditionally, the term control plane refers to the logic responsible for deciding how a network device should forward packets. The forwarding is done by fine-tuning the forwarding tables in the device data plane. In software-defined networking, the control plane is also a central point - the so-called network operating system (NOS) - from which network is managed globally. The network is understood as a collection of various physical and / or virtual devices that are controlled using different protocols: e.g. OpenFlow, Netconf, P4Runtime, BGP, PCEP etc.
Some common networking terms clearly explained