"Modern" feminism started in the 1880s or so with the Suffragettes. The latest wave hit in the late 1960s, as I was coming of age in the world; it was like having a noose suddenly removed from my neck, and breathing again.

I've always used a very simple definition:
Feminism believes that we are all created equal in the eyes of God, and no man has the right, by law or custom, to take away what God has given.