The quadrilateral is any 4-sided polygon.
But it is the parent of a whole family of figures, each with their own distinct names and characteristics.
See also Tetragon.
Quadrangle ("four angles") is another name for a quadrilateral.
However, it is a word often used for an open space where people gather, say on a school or university campus.
In this case the quadrangle (or "quad") is usually a rectangle or square.
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