The visual elements (buttons, menus, screens) that let you interact with software. Like the dashboard and controls in a car that help you drive.
The home screen of your phone, with its icons and menus, is a user interface that helps you access different apps.
“User Interface” (UI) is a general software concept, not a single cloud service. All major cloud providers offer consoles, dashboards, and UI-building tools, but there is no one-to-one managed service named “User Interface.”