Secular humanism is philosophically naturalistic. It holds that nature (the world of everyday physical experience) is all there is, and that reliable knowledge is best obtained when we query nature using the scientific method. Naturalism asserts that supernatural entities like God do not exist, and warns us that knowledge gained without appeal to the natural world and without impartial review by multiple observers is unreliable.
Secular. “Pertaining to the world or things not spiritual or sacred.”
Humanism. “Any system of thought or action concerned with the interests or ideals of people … the intellectual and cultural movement … characterized by an emphasis on human interests rather than … religion.”
— Webster’s Dictionary