With the package, \_ in text mode (i.e., \textunderscore) prints an underscore so that hyphenation of words either side of it is not affected; a package option controls whether an actual hyphenation point appears after the underscore, or merely a break point.

The package also arranges that, while in text, ‘_’ itself behaves as \textunderscore (the behaviour of _ in maths mode is not affected).

The author is Donald Arseneau. The package is Copyright © 1998,2001,2005,2006 Donald Arseneau.