Feminism is a movement which seeks respect and equality for women both under law and culturally.
Although improvements have been made, particularly in the last 50-100 years, women do not yet have full respect and equality. Overall, our society still has a systematic bias against women.
Feminists come in all shapes, sizes, colours, and genders. (Yes, men can be feminists.) There is likewise a wide range of political thought and ways of expressing feminism. Not all feminists think alike, but if you support the idea of respect and equality for women, then you are a feminist.