Before you start processing forms, you must describe the forms—what they look like and what type of information they contain – to FORMS. You do this by using the Manager to create form definitions.
A form definition contains a field definition for each area of the form where data is to appear or be filled in. In addition, there are a couple of other field types that do not contain interpretable data. (List of field types)
The field definitions are necessary for all other FORMS modules, and carefully prepared field definitions result in high interpretation rates and reduced verification work.