Usability
Usability is the ease with which a user can interact with a product or system to achieve their goals effectively and efficiently.
User Experience
User Experience (UX) is the overall experience and satisfaction a user derives from interacting with a product or service.
User Interface
A user interface (UI) is the point of interaction between a user and a digital device or software application.
Utility Function
A utility function is a mathematical representation of a consumer's preference ranking over a set of goods or services.