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 angle C:

enter image description here

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    No exciting term, it's just a small square. – Minnow Nov 17 '15 at 17:30
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    Or you could call it the "right-angle symbol". Not heard of a particular term for it though. – AndyT Nov 17 '15 at 17:32
  • It's called a corner. – LexieLou Nov 18 '15 at 3:32
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    @LexieLou Really? Do you know of a dictionary that includes this definition of "corner"? Thanks! – SAH Nov 18 '15 at 20:12

There is no name for it. The literal interpretation would be 90 degree angle.

It is a special case of the markers that denote the angle between two rays. For example, you could use an angle arc(shown as theta in your image) and beside it specify that its value is 90. Those two symbols would be equivalent.

  • Pardon my pickiness, but the literal interpretation need not be "90 degree angle"; the same symbol can be used to denote an angle that measures π/2 radians. Also, I remain unconvinced that there is no name for this symbol! – SAH Nov 27 '15 at 10:00
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    It can also be used to denote that two line are perpendicular. However, all of these are equivalent. The necessary condition being the exact value of the described angle. Also, this is EL&U. Being persnickety is almost a requirement :) – TsSkTo Nov 30 '15 at 21:54
  • @SAH 90° and π/2 are the same measurement expressed in different units. It's the same as 0°C and 32°F. Water freezes at that temperature however you express it. Just because π is an irrational doesn't mean it's not an exact number, just that you can't write it down exactly in digits. – BoldBen Oct 27 '16 at 8:29

I refer to it as just "right angle" or "right angle symbol". The same language is used in a number of places online, like Symbols in Geometry and the Wikipedia Right Angle article.

After reading the Wikipedia article, it may be necessary to distinguish the 'English' right angle symbol from the 'European' right angle symbol of an arc with a dot. I'm not sure that 'European' is exactly the right word to use, but I wasn't able to turn up any results for that symbol with a search. There is a UNICODE symbol, "right angle with arc": ⊾ but there's no dot there, so I don't think it's the same thing.

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    At TEX.SE, they called it a right angle symbol. – Mazura Apr 22 '16 at 3:53

Quadrant (n = 4)

The quadrant is 1/4 of a turn, i.e. a right angle. It is the unit used in Euclid's Elements. 1 quad. = 90° = π/2 rad = 1/4 turn = 100 grad. In German the symbol ∟ has been used to denote a quadrant.

–Wiki: Angle (emphasized)

At TEX.SE, they're colloquially called a right angle symbol. In the code however, it's called a right angle quadrant.

  • Is the symbol ∟ (used in-line in text) really the same thing as the square symbol found in these diagrams? – herisson Apr 22 '16 at 4:10
  • @sumelic - In "American" it's a little square. In "British" it's an arc with a dot (see Colleen's answer). In German, it's a ∟. All of these symbols represent a right angle quadrant. – Mazura Apr 22 '16 at 4:20
  • The arc with a dot is used in German speaking countries and Poland according to Wikipedia, not Britain. I only have experience with the American usage. @sumelic – ColleenV Apr 22 '16 at 11:28
  • @Mazura I''m British, I don't think I've ever seen the arc-with-a-dot and certainly wouldn't recognise it as a right angle. – BoldBen Oct 27 '16 at 8:35

Perhaps it is the Unicode character U+221F Right Angle, although a few other mathematical angle characters exist. See http://www.fileformat.info/info/unicode/block/mathematical_operators/images.htm.

You might also look at the four corner symbols, U+231C Top Left Corner, U+231D Top Right Corner, U+231E Bottom Left Corner, and U+231F Bottom Right Corner

Did some more looking at unicode and found U+299C Right Angle Variant with Square and U+299D Measured Right Angle with Dot

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