[jbeda]

A Pod manages a set of containers on a node.

A ReplicaSet (RCs are old and deprecated) manages a set of Pods. It has a template and a target replica count.

A Deployment manages ReplicaSets across versions/upgrades. When you change a deployment it creates a new ReplicaSet and does a rolling upgrade from new to old version by tweaking replica counts in new and old ReplicaSets.