FUNCTION

The underscore is essentially used today as a marker to separate words whenever spaces are not valid (URLs or email addresses, file names, etc.).

HISTORY

In European book publishing conventions, to underscore a word or sentence in a manuscript was meant to inform the typographer and/or printer to set it in italic (or in roman) style.

The symbol has been kept on typewriters and our contemporary keyboards for various uses in different languages, as an individual sign instead of being a mark combined with other glyphs.

DESIGN

The underscore is a dash-like glyph placed below the baseline and has (usually) the length of the en dash.

TYPOGRAPHIC RULES

There is no space on both sides of the underscore.

NOT TO BE CONFUSED

Commonly, we call this glyph the underscore. But, its ‘proper’ name should be the low line (as it is called in the Unicode naming with its correct code), because the underscore (U+0332) is a combining diacritic symbol used in multiple African and Native American languages.