According to the Wikipedia article on the subject:

Secular humanism is a humanist philosophy that upholds reason, ethics, and justice, and specifically rejects the supernatural and the spiritual as the basis of moral reflection and decision-making. Like other types of humanism, secular humanism is a life stance that focuses on the way human beings can lead good, happy, and functional lives. The term "secular humanism" was coined in the 20th century to make a clear distinction from "religious humanism."