Generally, "gender" is used to refer to the social aspects of being a man, woman, girl, or boy, while "sex" is used to refer to the physical characteristics of bodies deemed to belong to men or women. This distinction came about in the 20th century due to feminists wanting to distinguish between the social and physical aspects of the category “woman.”

A common belief in Western societies is that gender and sex are both binary systems, meaning there are only two mutually exclusive categories to which all people are assumed to belong. We are often taught- both explicitly and subconsciously, and from a very young age- to associate these categories with specific characteristics. Most of us would have no trouble coming up with a list like this, even if we recognize the traits to be stereotypical and limiting:

When laid out in this comprehensive manner, we can recognize that the majority of people present with a mix of characteristics from both categories, with very few people aligning as "perfectly" feminine or masculine in every trait. Instead, in everyday interactions, we tend to make split-second assumptions about strangers’ gender and sex, based on very little information such as fat distribution, clothing and physical presentation, and vocal timbre and pitch.