In the context of this Model, an Interface

solves part(s) of a business Problem, and maybe
surfaces a Dialog, or otherwise some kind of usable Interface.

Discussion

An interface surfaces some Dialog(s), and provides some mechanism(s) for interaction with solution Feature(s). The primary mechanism supported will either be a GUI graphical user interface or a CLI command line interface. Whether surface via GUI or CLI, under the “covers” there can (and often will) be an API application programming interface, whether or not the API is published and supported by an available library.