A polygon with four sides and four vertices — a quadrilateral (includes rectangles, squares, etc.).
小学校の図形の問題で四角形の面積を求めた。
In elementary school geometry problems, we calculated the area of a quadrilateral.
この図形は四角形だが、対角線の長さが等しくない。
This figure is a quadrilateral, but the lengths of its diagonals are not equal.
CADソフトで四角形を描いて寸法を設定した。
I drew a quadrilateral in CAD software and set its dimensions.