In form categories the user can decide to add multiple layers on how multiple form of an application will be displayed in the web. There is no limit to how many levels the user can use. Eachform category represente a new folders in which the forms can be store.
This is particularly useful when an application contains multiple forms that are related to each other or needs to be use in a precise step.
For more information on how to add it in the form behaviour please Click here