Within react-controlled-form, we sometimes talk about form state. This is neither connected to the field data nor has it to do with React's component state.
Actually, form state is a built-in part of every Form and should only be used to store additional information. It exists to separate pure form data from semantic information.
It acts pretty similar to React's component state or Redux state in general, but is shipped with special APIs to ensure it is encapsulated with every form instance.
It can be especially useful when dealing with complex forms that have several different validation states that yield different validation messages while the form validity remains binary.