In mathematical analysis, a differentiability class is a classification of functions according to the properties of their derivatives. Higher order differentiability classes correspond to the existence of more derivatives. Functions that have derivatives of all orders are called smooth.

• Гладкость — в математике см. Гладкая функция
• Гладкость — философское понятие, введённое Платоном. См. Гладкость (понятие)