also: たかっけい
noun
Geometry term for a closed plane figure with three or more straight sides.
三角形は最も単純な多角形です。
A triangle is the simplest polygon.
この多角形の内角の
Find the sum of the interior angles of this polygon.
多面体 is a polyhedron (3D), while 多角形 is a polygon (2D).
From 多 (many) + 角 (angle) + 形 (shape).