A common mistake among certain people is to confuse minus with monus. These are not to be confused!

Where minus (−) is defined as

x − y = x + (− y)

where − y is the additive inverse of y, we define monus (∸ [U+2238]) as

x ∸ y = max {x − y, 0}

In other words, x ∸ y is x − y if x ≥ y, otherwise it is 0. This is particularly useful in systems where sign cannot be handled.

This symbol (which I, here, call monus, but can be referred to also as dot minus) is one type of obelus. Obeluses, or obeli, refer to a historical annotation mark used in ancient manuscripts or codices to denote that a word, line, or passage is questionable or in some other way notable.

In modern English, this historical annotation mark (and its different forms) has diverged in meaning:

÷

Division (U+00F7; nowadays, obelus has also come to directly mean this symbol), which is used to denote mathematical division (though a solidus is preferred as per ISO 80000-2) and sometimes subtraction;

†

Dagger, or obelisk (U+2020), which is continued to be used for the practice of obelism, but which was historically done with − (U+2212), ⨪ (U+2A2A), and ÷ (U+00F7);

⁒

Commercial minus (U+2052; not to be confused with percent [%; U+0025]), which is used to denote subtraction, or sometimes a negative remainder of a division operation;

⸓

“Dotted obelos” (U+2E13), which renders differently on different operating systems, browsers, and contexts (e.g., typefaces, &c.). I have found that it renders as follows on different operating systems:

Linux

Looks like the division symbol, ÷;

macOS and *BSD

Looks like the monus/dot minus symbol, ∸;

Windows

Looks like the commercial minus symbol, ⁒.

To differentiate monus from similar symbols, refer to the following:

∸

Monus (U+2238);

−

Minus (U+2212);

⸓

Dotted obelus (U+2E13; not always rendered the same);

߸

Nko comma (U+07F8);

⨪

Minus with a dot below it (U+2A2A);

܋

Syriac Harklean obelus (U+070B).