Use the Hidden input type to create a form field with a static or dynamic value that does not need to be visible to the user, but should be stored with each form submission.  Dynamic values can be generated using tokens.  This is also useful if you have a webform that collects information which must in turn be forwarded to a 3rd party service for processing.  The 3rd party service often will require a hidden key value to identify the form submission. 

In the Display section, you can choose whether the form value is actually secured (just inserted into the database upon submission) or an actual concealed HTML element on the rendered form.