noun
plane geometry
The branch of geometry dealing with flat two-dimensional figures.
平面幾何学では、三角形や円の性質を学ぶ。
In plane geometry, we study the properties of triangles and circles.
Solid geometry, dealing with three-dimensional figures, as opposed to the two-dimensional focus of 平面幾何学.
Compound of 平面 (plane, flat surface) and 幾何学 (geometry).