underline

An underline is a horizontal line drawn beneath a segment of text. It is used to emphasize words in handwritten or printed material and to indicate interactive elements in digital interfaces. In typography, the line typically sits just below the baseline of the letters, often extending to match the width of the emphasized text.

Underlining predates modern typographic emphasis such as italics. In manuscripts and early printing it served as a visual cue for emphasis when italic or bold type was unavailable. On typewriters, underlining often represented italics because the machine could not print them; the result was later carried into some digital workflows as a conventional form of emphasis.

Variants include single underline, double underline, and decorative forms such as dashed, dotted, or wavy lines. In digital typography, underlines are commonly generated with CSS text-decoration: underline or with the HTML 'u' element. Because links on the web are typically underlined, designers sometimes avoid underlining non-link text to prevent confusion and rely on other cues for emphasis, such as bold or color. Underlines can interfere with descenders and may reduce readability in long passages.

In print and typography, underlining remains a practical tool for emphasis in handwritten notes, captions, and some traditional layouts. In digital design, it is most associated with hyperlinks, and its use for emphasis is often discouraged in favor of italics or bold. See also emphasis, italics, bold, hyperlink.