A method for showing emphasis not usually used in modern typesetting. The advent of bold and italic faces make underlining a word almost obsolete. This method is still used though for certain types of titles, such as the names of court cases in the legal system ( Smith vs. Jones for instance).
To create a line at, or slightly below, the baseline of one or more letters, words, or sentences. Underlining is a method of adding emphasis. However, with the advent of bold and italic faces, it is less used today. See also BASELINE BOLDFACE EMPHASIS ITALIC UNDERSCORE
An underline is used in the label of a widget such as a button or a menu item to indicate the presence and value of a mnemonic. In PHP-GTK 2, mnemonic support is enabled by default, so that a menu item with the label text _Save will automatically have as its keyboard shortcut. You can switch off this default behaviour when constructing simple widgets such as GtkButton and GtkMenuItem, or alternatively use a double underscore __ in order to display a single one where mnemonic support is present. See also: Accelerator, Mnemonic.
An underline is one or more horizontal lines immediately below a portion of writing. Single, and occasionally double, 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.