Website Forms are forms that are available on the front end of the event or form.  These are what individuals who are filling out a form online would be able to see and give responses to.

Sphere Entry Forms are the forms available through Bookkeeping in the back end of Sphere.  These forms are what would be filled out by someone in your organization when doing a registration entry, donation entry, etc., that isn't taking place on the front end of the event or form.