What does "二次元" mean?

动漫世界。与三次元，即现实世界相对。 该用法始于日本，早期的日本动画、游戏作品都是以二维图像构成的，其画面是一个平面，所以被称为是“二次元世界”，简称“二次元”。

ENThe world of anime and manga. As opposed to the three-dimensional world, i.e., the real world. This usage originated in Japan. Early Japanese animation and game works were composed of two-dimensional images, and their screens were a plane, so they were called 'two-dimensional worlds,' or 'two-dimensional' for short.