The vertical bar, |, is a glyph with various uses in mathematics, computing, and typography. It has many names, often related to particular meanings: Sheffer stroke (in logic), pipe, bar, or (literally, the word "or"), vbar, and others.

The vertical bar is used as a mathematical symbol in numerous ways. If used as a pair of brackets, it suggests the notion of the word "size". These are:

Likewise, the vertical bar is also used singly in many different ways:

The double vertical bar, ${\displaystyle \|}$, is also employed in mathematics.

In LaTeX mathematical mode, the ASCII vertical bar produces a vertical line, and \| creates a double vertical line (a | b \| c is set as ${\displaystyle a|b\|c}$). This has different spacing from \mid and \parallel, which are relational operators: a \mid b \parallel c is set as ${\displaystyle a\mid b\parallel c}$. See below about LaTeX in text mode.

In chemistry, the vertical line is used in cell notation of electrochemical cells.

Example,

Zn | Zn²⁺ || Cu²⁺ | Cu