Rectangular means shaped like an oblong with four right angles. A rectangular room, rectangular tables, roughly rectangular.
Strictly a square is rectangular too, since a square is a rectangle with equal sides, though nobody says so in ordinary speech. It is the shape almost every made object defaults to, because it packs and cuts without waste.
1adjectiverectangularShaped like an oblong with four right angles.
“We ate at a long rectangular table that seated the whole family.”
rectangular is a shape.