The term "sex" in "sex segregation" refers to apparent biological distinctions between men and women, used in contrast to "gender". The term "segregation" refers to separation of the sexes, which can be enforced by rules, laws, and policies, or be a de facto outcome in which people are separated by sex. Even as a de facto outcome, sex segregation taken as a whole can be caused by societal pressures, historical practices, and socialized preferences. Sex segregation can refer to literal physical and spatial separation by sex. The term is also used for the exclusion of one sex from participation in an occupation, institution, or group. Sex segregation can be complete or partial, as when members of one sex predominate within, but do not exclusively constitute, a group or organization.
In the United States some scholars use the term “sex separation” and not sex segregation". :229 
The term gender apartheid (or sexual apartheid) also has been applied to segregation of people by gender, implying that it is sexual discrimination. If sex segregation is a form of sex discrimination, its effects have important consequences for gender equality and equity.
A sign mandating sex segregation on a women's only car in India.