Intersectionality is defined as the interconnected nature of social categorizations such as race, class, and gender as they apply to a given individual or group, regarded as creating overlapping and interdependent systems of discrimination or disadvantage.
Individuals do not fit neatly within any one category, but live as people with racial, gendered, abled and sexual identities, privileges and forms of oppression are interlinked and cannot be addressed alone.
The relationship between a person’s various social identities is more important than a single social identity when it comes to implementing social justice. For example, one might be an upper middle class black cisgender (i.e., assigned female at birth, and still identifying as female) straight woman. This individual would experience life as a woman, as a black person, as a cisgender person, as a straight person, and as an upper middle class person at the same time while importantly also facing oppression because of the interaction of these identities.
In other words, social identities are not additive, they are intersectional, much like a traditional Venn diagram where various characteristics overlap to create a particular individuals’ identity.