Key Terms Every Editor Should Know

Updated March 24, 2026

CMOS Glossary in the Spotlight

In editing as in life, things tend to come in pairs. Life has its ups and downs, left and right, sea and land, victory and defeat. In editing you have capitals and lowercase, justified and ragged right, insert and delete.

A lot can be learned about a subject by considering terms that mean the opposite of each other or that are related in some other way. So we turned to CMOS in search of such pairs, starting with the glossary of key terms toward the end of the book. We found lots of connections, starting with terms related to letters and numbers.

The Right Type

Practically no one spends more time examining letters and numbers on a page or screen than editors do. It can help to know something about those shapes you’re staring at all day long.

typeface v. font. Most people these days use typeface and font interchangeably. Strictly speaking, however, Times New Roman and Adobe Caslon and the like are typefaces—a collection of fonts with a common design. Font, then, refers to a specific style of type at a specific size—for example, twelve-point Times New Roman regular or eighteen-point Adobe Caslon semibold italic.

Editor’s takeaway: From Microsoft Word to Adobe InDesign to WordPress—and pretty much everywhere else editors do their work—a typeface is generally called a font (or, in the HTML you’re reading right now, a font family). Unless you’re editing a book on type design, you can knowingly disregard the difference between the two terms. In this post, we’ll use font when we need to refer to one or the other.

old-style v. lining figures. Old-style figures (also called text figures) resemble letters. (Note that a figure in this context is a number expressed as a numeral.) Like letters, old-style figures feature ascenders and descenders, as in the stem on a lowercase d (an ascender) or the tail on a lowercase p (a descender). In the following example featuring Source Serif (a Google font that also includes lining figures), note the descenders on 3, 4, 5, 7, and 9 and the ascenders on 6 and 8:

Lining figures, on the other hand, resemble letters in all caps. (Lining figures, which are also called modern figures, emerged somewhat later than old-style figures in the history of printing and typesetting.) Instead of featuring ascenders and descenders, lining figures align at their tops and along the baseline, the imaginary line that all letters and numbers rest on. Here’s an example in Source Serif:

Editor’s takeaway: Depending on the font, a zero in old-style figures can look like the letter oh, and a one may look like a Roman numeral one (though not in Source Serif). Being aware of this can help you know to recommend lining figures—or words rather than numerals—for contexts where old-style figures may be ambiguous (something that proofreaders, too, can look out for).

monospaced v. proportional. In a monospaced (or fixed-width) font, each letter, number, or other character (including punctuation) takes up the same amount of space. For example, in Courier New, a popular font designed to mimic a typewriter, the ten-letter synonyms Copyeditor and Amanuensis are of equal length:

In a proportional font (Source Serif again), they are not; note, for example, how the letter i is narrower than the letter m:

A related concept applies to figures. The numbers in a proportional font are often proportional like letters, but a font may also feature tabular figures (whether as old-style or lining figures) in which each digit from 0 through 9 takes up the same width (as in a monospaced font). They’re called tabular figures because they’re designed to line up in the columns of a table (where tabular lining figures are usually preferred for their combination of vertical and horizontal uniformity).

Editor’s takeaway: Normally you won’t have to worry about proportional versus monospaced, but if you notice that the figures in a table aren’t lining up properly (especially along the decimal), you may suggest that tabular (monospaced) figures should be used instead of proportional.

serif v. sans serif. A serif is a small projecting line or wedge on the main stroke of a letter. Most fonts used for the text of published books have serifs. Sans serif fonts, as the name suggests, don’t have these extra bits. Here’s what that looks like (in Source Serif and Microsoft Aptos, respectively):

Editor’s takeaway: Opinions differ about when to use serif or sans, so the decision is best left to a design pro. But editors might run across a case in which a sans serif font isn’t the best choice—for example, if the meaning of the text depends on being able to see the difference between a capital I (as in the first-person pronoun) and a lowercase l (el). For this reason, many editors prefer serif fonts at the manuscript stage.

kerning v. letterspacing. Letterspacing, also known as tracking, refers to the average space between letters and other characters in a line of type. In justified text (covered below), letterspacing may be adjusted to allow the letters to fill out the line—though not to the degree shown in the first two lines in the following example:

Kerning, on the other hand, refers to a specific instance of letterspacing between two adjacent characters that may overlap. Note in the following example how the serif on the V overlaps with the o in the first line (in proportional Source Serif) but not in the second (in monospaced Courier New):

In this context, the serif on the V is also known as its kern.

Editor’s takeaway: Proofreaders, who usually work with text that’s been edited and formatted for publication, will especially want to watch for and flag lines that are too obviously loose or tight—as in justified text (see next item). Hyphenation and other adjustments may be necessary to allow for better spacing.

justified v. ragged right. Text that’s justified (in what is also referred to as full justification) aligns on both the left and the right margins. Justified text depends on automatic adjustments to the space between letters and words. Text with a ragged right margin (like the text in this post) doesn’t require any such adjustments.

Editor’s takeaway: Justified text requires paying extra attention at the proofreading stage to lines that may be too loose or too tight. With a ragged-right (or -left) margin, on the other hand, the words fall where they fall (though the occasional adjustment may be warranted, especially if hyphenation is an option).

More Pairs

Did you know each of the terms above? Here are a few more.

insert v. delete. In pencil-edited copy, editors draw a caret (^) to show where to insert text, which is in turn written in wherever there is space to do so. Deletions are struck through with a line, sometimes with a loop at the end of it. In MS Word and the like, markup is automatic—for example, inserted text gets underlined, like this, whereas deleted text is struck through~~, like this~~. (For a detailed overview of the editing process, both on paper and on the screen, see chapter 2 in CMOS.)

redline v. blackline. The terms redline and blackline both refer to a document that’s been marked up to show changes. Redline invokes the editor’s red pencil (though it’s now more likely to apply to documents edited in Word or the like that include tracked changes). Blackline is common in law (where a document that’s been marked to show changes relative to an earlier version may be called a legal blackline). Many editors use the term redline to refer to any marked-up document.

editor’s style sheet v. electronic style sheet. An editor’s style sheet is a list that specifies for proofreaders and others who will be reviewing a document how certain words should be spelled, whether to use serial commas, and other matters related to editorial style. An electronic style sheet, on the other hand, is a set of programmatic instructions that applies font styles, indents, and other formatting attributes to a document intended for the screen. Web pages and ebooks typically rely on CSS (cascading style sheets) in conjunction with HTML (hypertext markup language).

HTTP v. HTTPS. HTTP stands for “Hypertext Transfer Protocol,” a standard that supports the hyperlinked pages of the internet. HTTPS (the S stands for “Secure”) adds a layer of encryption and other security mechanisms. A URL that begins with http:// will usually redirect to an https:// version (most sites now use https).

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Other pairs include typesetter v. compositor (which are synonymous); vector graphic v. bitmap (vectors are smooth at all sizes, whereas bitmaps lose clarity as they are enlarged); cloth v. paper (as in hardcover versus paperback books); ASCII v. Unicode (old-school character encoding versus modern); widow v. orphan (the first line of a paragraph stranded at the bottom of a page is an orphan; a widow is a short last line stranded at the top of a page); SMALL CAPS v. ALL CAPS (as illustrated here); subscript v. superscript (as in H₂O or E = mc²); and Arabic v. Roman numerals (3 versus III).