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
Kids Math: Square and Square Root
What Is A Square Number: Explained For Primary School Parents & Kids
Square (algebra) - Wikipedia
Right angle - Wikipedia
Reciprocal - Definition & Examples
Diacritic - Wikipedia
Math Dictionary For Kids: Essential Guide to Math Terms!
In geometry, what does the upside down 't' mean? - Quora
What does a large, U-shaped symbol indicate in mathematics? - Quora
Interval in Math, Definition & Examples - Lesson
Area of a Square Area of a Square = (Side × Side) Square Units