I have never seen the worker nodes & associated components referred to as the "data plane" before. Looking it up, it looks like Spot (spot.io) and Kong have done it before. In the Kong article where they call it the "data plane" they do say explicitly "Within the Kubernetes context, worker nodes (with their pods and containers) make up what we've defined as a data plane." No docs from the Kubernetes project use the term "data plane" though. I feel like "data plane" could be better used to describe storage technologies your Kubernetes cluster might interact with, since the worker nodes are really about compute, not data.