Diacritic comes from the Greek, meaning distinguishing. They are marks which modify a glyph. The term diacritic is the formal typographic term for accents. The most common ones known to Canadians are French accented characters. So we can say we’re typing diacritics, or diacritical marks.
Most diacritics in english are borrowed from the French. There’s résumé, café, and façade, for instance. The accents are sometimes omitted in written English.
To type these on macOS, you simply need to hold down the letter on the keyboard. In macOS apps, the contextual menu will appear. Each entry is numbered. Just type the number to choose one.
Some applications, like Adobe apps, don’t support the contextual menu. In these circumstanced, you can type the following;
Option-e then e, for é
Option-` then e, for è
Option-i then e, for ê
In the head of your HTML document, be sure to set the character encoding to UTF-8 like this;
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
That will allow you to simply type the glyphs as shown above. They’ll appear properly on your pages. This is because glyphs such as é are included in the UTF-8 character set.