The ramp function is a unary real function, whose graph is shaped like a ramp. In machine learning, it is commonly known as the rectifier used in rectified linear units (ReLUs). It can be expressed by numerous definitions, for example "0 for negative inputs, output equals input for non-negative inputs". The term "ramp" can also be used for other functions obtained by scaling and shifting, and the function in this article is the "unit" ramp function (slope 1, starting at 0).