An overline is a horizontal line placed above a mathematical symbol or expression. A short accent over a single character, such as 
,
is called a macron, while a line spanning an expression,
such as 
, is called a vinculum.
The names bar, overbar, and overline overlap in usage and
do not impose a strict single-character versus whole-expression distinction (Unicode
Consortium 2026, p. 10).
An overline may cover a single base symbol, as in 
,
or the entire indexed expression, as in 
. In graph
notation, these forms may denote the same graph complement
(Gross et al. 2014, p. 53).
