Alt

Alt is a compact term that appears across languages and disciplines with several distinct meanings. In Germanic languages, 'alt' means old. In English, the same letters are often used as a short form of 'alternative' or 'alternate' in contexts such as 'alt-season' or 'Alt UI' and in guidance like 'Alt key'. In science and technology, 'alt' frequently appears as a root in words derived from Latin altus meaning high, as in altitude, altimeter, or altissimo; as an acronym, ALT can denote various phrases depending on domain.

In computing and devices, Alt refers to the Alt key on keyboards, used with other keys to issue shortcuts, access menus, or produce special characters. On many keyboards there is an AltGr key that enables third-level characters; many systems provide 'Alt codes' by holding Alt and typing a numeric code to insert a character.

In HTML, the alt attribute of the img element provides alternative text; it is used by screen readers to describe images and as a fallback if the image cannot be loaded. Good alt text should be concise and descriptive.

In music notation, particularly in German-language contexts, 'Alt' denotes the alto vocal range, equivalent to the English 'alto' or 'contralto' in choral parts.

In aviation and meteorology, ALT is a standard acronym for altitude on charts and instruments. The term also appears in education, branding, and culture as a shorthand for alternative or experimental concepts, reflecting its flexible usage across fields.