Here are a few definitions of "Humanism" from the American Humanist Association.
Humanism is a progressive lifestance that, without supernaturalism, affirms our ability and responsibility to lead meaningful, ethical lives capable of adding to the greater good of humanity.
American Humanist Association
Humanism is a rational philosophy informed by science, inspired by art, and motivated by compassion. Affirming the dignity of each human being, it supports the maximization of individual liberty and opportunity consonant with social and planetary responsibility. It advocates the extension of participatory democracy and the expansion of the open society, standing for human rights and social justice. Free of supernaturalism, it recognizes human beings as a part of nature and holds that valuesbe they religious, ethical, social, or politicalhave their source in human experience and culture. Humanism thus derives the goals of life from human need and interest rather than from theological or ideological abstractions, and asserts that humanity must take responsibility for its own destiny.
The Humanist Magazine
Humanism is a democratic and ethical lifestance which affirms that human beings have the right and responsibility to give meaning and shape to their own lives. It stands for the building of a more humane society through an ethics based on human and other natural values in a spirit of reason and free inquiry through human capabilities. It is not theistic, and it does not accept supernatural views of reality.
The International Humanist and Ethical Union
http://www.americanhumanist.org/humanism/definitions.htm