Sexism is unfair treatment of people based on whether they're male or female. When someone practices sexism, they make assumptions about what people can or should do simply because of their sex, rather than looking at their actual abilities, interests, or character.

Sexism can work in different directions. Historically, it most often meant treating girls and women as less capable or intelligent than boys and men. For example, there was a time when people believed girls couldn't handle advanced mathematics or shouldn't become doctors, which was completely wrong. Some people still hold sexist views today, like assuming a boy can't be a skilled dancer or a girl can't be good at fixing cars.

Sexism appears in many forms. It might be a teacher who always calls on boys to answer science questions but asks girls about art. It might be someone saying “you throw like a girl” as an insult, which is sexist because it assumes being female means being weak. It might be paying someone less money for the same work because of their sex.

The opposite of sexism is treating people as individuals, recognizing that abilities and interests vary from person to person, not by whether someone is male or female. When you evaluate someone based on their actual skills, character, and effort rather than making assumptions about their sex, you're avoiding sexism.