The word humanism, in its current sense, was first used in mid 18th century France and roughly meant "A general love of humanity." Today, the American Humanist Association defines humanism as
[...] a progressive philosophy of life that, without theism and other supernatural beliefs, affirms our ability and responsibility to lead ethical lives of personal fulfillment that aspire to the greater good of humanity.Does that mean that a humanist cannot have theism and supernatural beliefs, or does it mean that a humanist just doesn't use supernatural beliefs to guide his/her ethical life?
Now, the word "secular" is a little less vague. It means, roughly, separate from religion, or only pertaining to worldly things.
Another word that we hear often when talking about atheism, humanism, etc., is agnosticism. Agnosticism is the belief that supernatural claims cannot be proven or disproven with the current set of data (or potentially at all, ever). By that definition that would certainly make most Christians agnostic (it is all about faith, right?) and it certainly makes atheists agnostic. We cannot truly claim to know God does not exist, can we? Colloquially, agnosticism is used to suggest one's own doubt about whether or not a claim is true.
However, the most important definition of a word comes from how people actually use it. How do you identify yourself? What do these words mean to you when you hear them? Is "secular humanism" a redundant term, or can there be religious humanism?