What's the difference between @minus and minus?

When I look at different uses of glue in spacing, I see both \@minus and minus.

What's the difference between \@minus and minus?

• latex format define \def\@minus{minus} – touhami Sep 5 '15 at 19:48
• Nothing really. In the old days \@minus just saved a few things in Texs memory (or something like that, there is a word for what was saved, but I've forgotten it) – daleif Sep 5 '15 at 19:48

The expansions of \@minus and \@plus are, respectively, minus and plus. But \@minus counts as one token in the replacement text of a macro, whereas minus counts as five.
Now, \@plus appears 16 times in latex.ltx (one is the definition), 15 times in article.cls and 36 times in size10.clo, which makes for a saving of (15+15+36)*(4–1) = 198 tokens on every standard document in the article class. This might appear ridiculous nowadays, but, when LaTeX2e was released, memory was really scarce and even such savings were worthwhile. There are several other token saving tricks such as \z@, \p@, \hb@xt@ and so on, which (on some TeX distributions) made the difference between being able to run LaTeX or not.