Hidden data identifies a quality that describes the entire form. For example, hidden data might identify the information as being from an online application instead of a hard-copy application.

Custom data typically identifies a quality that describes only one row, or set, of data in the form. For example, if your form is going to insert data into a table that is capable of storing both home and work addresses and the form asks for both home and work address, you can use custom data to identify which set of questions should be associated with the home address code and which set of questions should be associated with the work address code