User Interface (UI)
Definition:
User interface is how a user interacts with and controls a piece of machinery such as a computer.
A good user interface experience is intuitive, efficient and enjoyable to operate and makes it easy for a user to achieve a desired result. Generally, the less input needed to achieve a desired result, the better.
User Interfaces can include a number of layers. An example of this is a Human Interface Device (HID). These allow for physical interactions with machines. Examples include a mouse, keyboard, touchscreen, monitor, gamepad, microphone or even speakers.
Graphical User Interface (GUI)
A Graphical User Interface is a collection of interactive, visual components and elements that make up a piece of computer software. A GUIs main purpose is to display and convey information and provide actions in which a user can take. It enables users to interact with and control a piece of software without knowing computer command language.
GUI elements include icons, cursors, sounds, menus, windows, buttons and more.