In an IT system, a User Interface (UI) is the central interaction point with the user. This could be a display, a mouse or keyboard or a graphical software user interface. Since the UI is the entrance to a whole system, it should mirror all the system individual components and provide an interaction level for each of them (at least for the ones which need an interaction with the user).
Since CREMA builds a holistic system consisting of multiple interactive components, following user interfaces enabling the interaction with the user are needed:
General definition of a Graphical User Interface: https://www.computerhope.com/jargon/g/gui.htm