Heaviside step function (H), or the unit step function, is a mathematical function that is defined as:
H(x) = 0 for x < 0
H(x) = 1 for x ≥ 0
It is named after Oliver Heaviside, who introduced it in the late 19th century. It is often used to model the behavior of systems that switch on and off in fields such as electrical engineering, control systems, and signal processing.