21 CFR 335.3 - Definitions.
As used in this part:
(a) Antidiarrheal. A drug that can be shown by objective measurement to treat or control (stop) the symptoms of diarrhea.
(b) Diarrhea. A condition characterized by increased frequency of loose, watery stools (three or more daily) during a limited period (24 to 48 hours), usually with no identifiable cause.
(c) Travelers' diarrhea. A subset of diarrhea occurring in travelers that is most commonly caused by an infectious agent.