二维空间或译二度空间（Second Dimension）是指仅由宽度→水平线和高度→垂直线（在几何学中为X轴和Y轴）两个要素所组成的平面空间，只在平面延伸扩展，同时也是美术上的一个术语，例如绘画便是要将三维空间的事物，用二维空间来展现。

若把三维空间压扁成二维，物质会变得非常薄，重力的行为也会改变，重力不需要通过空间来传播，基本上二维重力根本无法传播。反之，重力能驱使空间的形状改变。

In physics and mathematics, two-dimensional space or bi-dimensional space is a geometric model of the planar projection of the physical universe. The two dimensions are commonly called length and width. Both directions lie in the same plane.

A sequence of n real numbers can be understood as a location in n-dimensional space. When n = 2, the set of all such locations is called two-dimensional space or bi-dimensional space, and usually is thought of as a Euclidean space.