Underline

An underline, also called an underscore, is one or more horizontal lines immediately below a portion of writing. Single, and occasionally double ("double-underscore"), underlining was originally used in hand-written or typewritten documents to emphasise text. In a manuscript to be typeset, various forms of underlining were conventionally used to indicate that text should be set in a special typeface such as italics to show emphasis, part of a procedure known as markup. With the advent of word processing, different typefaces can be used in the manuscript directly, so that underlining is no longer needed for markup; but underlining is sometimes used in documents in its own right.