This word means "one person." It is also used to express being "alone" or "by oneself." It is an irregular reading for counting people, specifically for the number one, differing from the regular "いちにん."

「一(いち)人(にん)」を意(い)味(み)し、単(たん)独(どく)でいる状(じょう)態(たい)も指(さ)します。人(にん)数(ずう)を数(かぞ)える際(さい)の特(とく)別(べつ)な読(よ)み方(かた)です。