Discrimination is difficult to qualify in an abstract sense—how does one qualify all of the accepted categories of sex, religion, ethnicity, etc. into a single definition? Something like ethnicity is something no one can choose and no one can change. On the other hand, religion is a choice of belief and values that has been deemed protected under our freedom of religion. It’s hard to determine what, other than our society’s values, has decided which categories are protected from judgment.
As it applies to gender, however, discrimination is the differential treatment of a person based on an uncontrollable element of their identity. Holding a woman to a different standard than a man or treating them unequally, such as a woman being paid less than a man despite having the same education and experience background in a job, is discrimination. Unfortunately, this is one of the least “marked” forms of discrimination in our society, because so many have internalized the judgments, stereotypes, and stigmatizations of our gender system that they don’t even consciously recognize their sexist attitudes. This is what makes feminism necessary—to challenge and help people realize that despite their beliefs about themselves, they have deep-seated discrimination against women.