Social gender, often referred to simply as gender, is a social construct that assigns people to social groups based on their characteristics. In Western culture, there are two main social genders; masculine and feminine, which are strongly correlated with but distinct from biological sex.
Social gender is reflected in language through grammatical gender. English speakers tend to use he pronouns to talk about masculine people (men and boys), and she pronouns to talk about feminine people (women and girls). This is actually the secondary gender system in English.
Gender-neutral language is an alternative to expressing social gender.