The Generic Input Form is basically a custom form to enter data for a SharePoint list. It is in fact a customizable webpart which can be placed on any page. Properties of the webpart include layout, colours, borders and usage of lists and fields. 

The user can enter data and save this to one or multiple lists. The form looks like a normal SharePoint input form, but differs in a sense that it contains data entries from multiple lists. That way, the user processes only one form and in the background fills in all related lists.