Event Handler: An event handler is a block of code that responds to a specific program event. It is responsible for executing the desired actions when the associated event occurs.
User Interface (UI): The user interface refers to the visual elements and controls through which users interact with a computer program. Program events often occur as responses to user interactions with the UI.
Event-driven Programming: Event-driven programming is a programming paradigm where the flow of execution is determined by events and their handlers. It allows programs to respond dynamically to various events rather than following a predefined sequence of steps.