vocabulary - I need a word to describe the quality of a rectangle

I would like a more formal word that describes the rectangle on the left as opposed to the slanted one on the right. For some reason, I can't seem to think of a description without being wordy

What is a Rectangle?, Rectangle Shape

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What is Rectangle? Definition, Examples, Formula, Facts

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What is Rectangle? Definition, Examples, Formula, Facts

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What is Rectangle? Definition, Examples, Formula, Facts

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Rectangle - Formulas, Definition, Examples