U+2381 CONTINUOUS UNDERLINE SYMBOL

U+2381 was added to Unicode in version 3.0 (1999). It belongs to the block Miscellaneous Technical in the Basic Multilingual Plane.

This character is a Other Symbol and is commonly used, that is, in no specific script.

The glyph is not a composition. It has a Neutral East Asian Width. In bidirectional context it acts as Other Neutral and is not mirrored. In text U+2381 behaves as Alphabetic regarding line breaks. It has type Other for sentence and Other for word breaks. The Grapheme Cluster Break is Any.

The Wikipedia has the following information about this codepoint:

An underline, also called an underscore, is a more or less horizontal line immediately below a portion of writing. Single and occasionally double ("double-underscore") underlining was originally used in hand-written or typewritten documents to emphasise text. In a manuscript to be typeset, various forms of underlining were conventionally used to indicate that text should be set in a special typeface such as italics to show emphasis, part of a procedure known as markup. With the advent of word processing, different typefaces can be used in the manuscript directly so that underlining is no longer needed for markup, but underlining is sometimes used in documents in its own right.

Underlines are sometimes used as a diacritic, to indicate that a letter has a different pronunciation from its non-underlined form.