This definition of mythology/myth is from the Bill Moyers program Joseph Campbell: Myths to Live By (Part One). It is dated April 17, 1981.
BILL MOYERS: What is a myth?
JOSEPH CAMPBELL: Well, let’s begin with what a mythology is. A mythology is a system of images that incorporates a concept of the universe as a divinely energized and energizing ambience within which we live. Do you understand what I am saying? And a myth, then, is a single story or a single element of the whole mythology, and the various stories of the mythology interlock — they interlock to be consistent within this great world image.