数学中，一个实数函数被称为阶段函数（或者阶梯函数），则它可以被写作：有限的间隔指标函数的线性组合。不正规的说法是，一个阶段函数就是一个分段常值函数，只是含有的阶段很多但是有限。
In mathematics, a function on the real numbers is called a step function (or staircase function) if it can be written as a finite linear combination of indicator functions of intervals. Informally speaking, a step function is a piecewise constant function having only finitely many pieces.