Wikipedia says:
Secular humanism is the branch of humanism that rejects theistic religious belief and the existence of a supernatural. It is often associated with scientists and academics, although it is not at all limited to these groups. Secular humanists generally believe that following humanist principles (active ethical philosophies that affirm the dignity and worth of all people, based on the ability to determine right and wrong by appeal to universal human qualities) naturally leads to secularism, on the basis that religious views cannot be supported rationally. There are secular humanistic organizations, though these could not be accurately described as churches.
More often than not, secular humanism is what people are referring to when they speak of humanism in general, making it something of a default. Some secular humanists take this even further by denying that religious humanists qualify as genuine humanists. Others feel that the ethical side of humanism transcends the issue of religion, because being a good person is more important than supernatural beliefs.