We often sort things into binaries, systems with only two categories. The categories often take the form of “this” or “not this.” For example, fiction and nonfiction. Free and priced. These labels sometimes work when there are clear-cut differences between inanimate objects. However, people are rarely so simple.
The gender binary is the idea that all people are either entirely male or entirely female. No exceptions, nothing in between. We’ll point out how that idea is flawed and how gender identity is much more colorful than black and white.