gender

One of the most fundamental distinctions made in Olympic sports (and others) is the division between men's and women's events.  Most sports on offer at the Games feature events that are divided into exclusively male or female categories.

(Some exceptions come to mind: rhythmic gymnastics and synchronized swimming are for women only, whereas Greco-Roman wrestling is for men only.  Men's and women's gymnastics involve some different equipment for men versus women.  Equestrian events are integrated.)