LigaTures

Ligatures are used in typesetting so that the printed text looks cleaner. Examples of ligatures are "fi" and "fl". When typesetting, "fi" and "fl" are actually separate characters that combine those two letters. Ligatures in groff are turned on by default, and they can sometimes cause problems when the groff-formatted document is used in other software (A groff postscript file in Adobe Illustrator, for example). You can turn off the ligatures by setting ".lg 0".

For more information see: http://olympus.het.brown.edu/cgi-bin/info2www?(groff)Ligatures+and+Kerning