This page describes notation conventions used in Emacs documentation. The EmacsManual provides a page of notation conventions but it does not cover everything.
Emacs documentation abounds with short phrases, usually command names (e.g., ‘next-line’) and key sequences (e.g. ‘C-x 4 f’), that are enclosed by two marks. See EmacsKeyNotation for more about the notation for key sequences.
The opening mark is accent grave or backtick (`). The ending mark is an apostrophe ('). The origins of this convention are uncertain, but an inquiry on the email list: help-gnu-emacs@gnu.org yielded these suggestions and ideas
`, ') were single quotes with curves inward. That is, they were symmetrical. Nowadays, the second of these (apostrophe) is typically vertical, not curved or slanted.The `...' notation dates from plain text-only communication: email etc. Keep in mind that Emacs still is mainly a plain-text editor. It still uses mainly fixed-width fonts by default, because it is mainly used with code, by programmers. The `...' convention is simple and clear. It is also easy to parse, and hence highlight – as is done on ThisWiki, for instance. – DrewAdams