mathematics - What's the word for the small square indicating a right angle in a geometric figure? - English Language & Usage Stack Exchange

I'm talking about something in geometry notation and/or drafting, I think. It's the mini right-angle shape you can draw within an angle to indicate that it's ninety degrees. E.g., the mark denoting

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The Semiotic Structure of Geometry Diagrams: How Textbook Diagrams Convey Meaning - National Council of Teachers of Mathematics

Why is Pythagoras'/Pythagorean theorem for 'Isosceles Standard/Right Triangle (IST)' suitable and actually provable from theoretical geometric perspective, but not factually suitable and provable from algebraic and practical holistic perspective? - Quora

Why is Pythagoras'/Pythagorean theorem for 'Isosceles Standard/Right Triangle (IST)' suitable and actually provable from theoretical geometric perspective, but not factually suitable and provable from algebraic and practical holistic perspective? - Quora