The grave accent ( ` ) is a diacritic mark used in written French, Catalan, Italian, Vietnamese, and other languages.
In French, the grave accent has two uses. On the letter e it marks the distinct quality of the vowel: è [E], and e [@]. It is also used as a grammatical mark, serving to distinguish between the preposition à ("to") and the verb a (present tense of avoir); and où ("where") and ou ("or").
In Catalan, the grave accent is used to mark both the stress and the distinct quality of certain stressed vowels, such as è [E] versus é [e], or such as ò [O] versus ó [o].
In Italian, it marks final stress, as in virtù ("virtue") or città ("city").
In Vietnamese and some other tonal languages, the grave accent is used to indicate a falling tone.
The grave accent is used in English only in poetry and song lyrics. It indicates that a vowel usually silent is to be pronounced, in order to fit the rhythm or meter. Most often, it is applied to a word ending with -ed. For instance, the word looked is usually pronounced as a single syllable, with the e silent; when written as lookèd, the e is pronounced -- look-ed.
Using the ISO-8859-1 character encoding, one can type the letters à, è, ì, ò, and ù. Dozens more letters with the grave accent are available in Unicode. Unicode also provides the grave accent as a combining character.
In the ASCII character set the grave accent is encoded as character 96, hex 60. Outside the US character 96 is often replaced by the local currency symbol. Many UK computers have the UK pound symbol as character 96.
Many of the UNIX shells use pairs of this character -- known as backquote -- to indicate substitution of the standard output from one command into a line of text defining another command.
In Lisp macro systems, the backquote character (called quasiquote in Scheme) introduces a quoted expression in which comma-substitution may occur. It is identical to the plain quote, except that symbols prefixed with a comma will be replaced with those symbols' values as variables. This is roughly analogous to the Unix shell's variable interpolation with
$ inside double quotes.