Simply put, feminism is a movement to end sexism, sexist exploitation, and oppression. This was a definition of feminism I offered in Feminist Theory: From Margin to Center more than 10 years ago.
It was my hope at the time that it would become a common definition everyone would use. I liked this definition because it did not imply that men were the enemy.
By naming sexism as the problem it went directly to the heart of the matter. Practically, it is a definition which implies that all sexist thinking and action is the problem, whether those who perpetuate it are female or male, child or adult. It is also broad enough to include an understanding of systemic institutionalized sexism.
As a definition it is open-ended. To understand feminism it implies one has to necessarily understand sexism."