What does being a feminist mean?

In her nonfiction work We Should All Be Feminists, Chimamada Ngozi Adichie discusses the demonization of the term feminism and how the movement benefits all people. Inspired by her famous TED talk of the same name, the book contains numerous explanations of what it actually means to be feminist.
Perhaps the quote from the text that best represents Adichie’s view is the following:

My own definition is a feminist is a man or a woman who says, yes, there’s a problem with gender as it is today and we must fix it, we must do better. All of us, women and men, must do better.

A feminist is someone who works to dismantle the harmful ways gender stereotypes impact both men and women in society. The reason that Adichie chooses the terminology of feminism is because she asserts that using a different word denies the reality that women and girls have been systematically disadvantaged more than their male counterparts. However, this does not mean that men and boys are excluded from participating in feminist causes. Rather, Adichie suggests that they will directly benefit from changing the ways in which the world categorizes and limits people based on their gender.