Configurable fields are typically created through the UI, attached to an entity type bundle, and exported to code. The part highlighted with bold is a critical difference between these and base fields in that base fields exist on all bundles of the entity type. You should already be familiar with the UI for creating a configurable field:
They also use the TypedData API for their definitions, as well as the same field type, widget, and formatter plugins we talked about earlier. Architecturally speaking, the main difference between base and configurable fields is that the latter are made up of two parts: storage configuration ...
