the.com/quadrilateral
A shape that picked four sides and stopped negotiating.
means Any flat closed figure with four straight sides and four corners, from squares to wonky kites.
from Latin quadri- (four) plus latus (side), so literally four-sided — geometry calling it exactly what it is.
Angle sumInterior angles always total 360 degrees.
Family treeSquares, rectangles, rhombi, trapezoids all qualify.
Diagonal trickTwo diagonals split it into triangles.