Mouse input refers to the method of controlling a computer's graphical user interface using a mouse. This device allows users to interact with on-screen elements by moving a pointer, clicking, and dragging. The primary functions include selecting items, opening files, and navigating through menus. When a user moves the mouse, sensors detect the movement and translate it into cursor movement on the screen. Clicking the mouse buttons sends commands to the computer, enabling actions like opening applications or executing commands. Overall, mouse input enhances user experience by providing a simple and intuitive way to interact with digital content.