Humanism is understood as an ethical and fulfilling non-religious approach to life involving a naturalistic view of the universe.
Roughly speaking, the word humanist has come to mean someone who:
trusts the scientific method when it comes to understanding how the universe works and rejects the idea of the supernatural (and is therefore an atheist or agnostic)
makes their ethical decisions based on reason, empathy, and a concern for human beings and other sentient animals
believes that, in the absence of an afterlife and any discernible purpose to the universe, human beings can act to give their own lives meaning by seeking happiness in this life and helping others to do the same.
Stephen Fry explains things from a Humanist point of view:
What makes something right or wrong?
How do we know what is true?
How can I be happy?
What should we think about death?