Overlines

An overline, also called an overbar or macron in some contexts, is a horizontal line placed above one or more characters. It appears in typography, linguistics, mathematics, and logic, serving different purposes depending on the field. The term overline may refer to the decorative diacritic macron when applied to vowels, or to a general horizontal line used in formal notation.

In mathematics, an overline is often called a vinculum. It is used to group terms, indicate the scope of an operation, or denote repetition in decimals: for example, 0.\overline{3} means 0.333... In logic, A̅ denotes negation (NOT A); in complex analysis, z̅ denotes the complex conjugate of z. In statistics and related fields, x̄ denotes a mean or average, and t̄ may denote a time-averaged quantity.

In linguistics and orthography, a macron is a diacritic placed above vowels to indicate length in many languages, such as Latin and Māori, and is common in phonetic transcription and dictionaries. The overline graphic is related but not identical to the function of the macron in language writing.

In computing and typography, overlines are produced with combining characters such as the Unicode COMBINING OVERLINE (U+0305) or via font-specific glyphs. TeX and LaTeX provide commands like \bar and \overline to render overlines, and CSS offers text-decoration: overline to display a line above text.

See also: macron, vinculum, negation, mean, complex conjugate, repeating decimal.