used to say that the total number of sb/sth is very small
BE ABLE TO COUNT SB/STH ON (THE FINGERS OF) ONE HAND
Meaning of BE ABLE TO COUNT SB/STH ON (THE FINGERS OF) ONE HAND in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005