Variable input refers to any type of data, information, or parameter that can change or be changed. This means that the input is not fixed and can be altered depending on different conditions or requirements. In the context of computer programming, a variable input is often a placeholder that stores values which can be modified during the execution of a program. Similarly, in mathematics, a variable represents an unknown or a value that can take on different numerical quantities within equations or functions. In experimental sciences, a variable input is a component of an experiment that is systematically manipulated to observe its effect on the outcome, helping to establish cause-and-effect relationships. The concept of variable input is crucial across various fields as it allows for flexibility, customization, and adaptability in processes, calculations, and analyses.