Gradient plane

Quick answer：

A gradient plane refers to a flat surface or a two-dimensional space that has a gradient or a gradual change in color, texture, or other properties. It is often used in art, design, and photography to create a sense of depth or to represent concepts like temperature, light intensity, or elevation. In mathematics, a gradient plane can also refer to a level surface of a three-dimensional function, where the gradient vector is perpendicular to the surface at every point.