I get into this debate every once and a while with fellow applicators. Some say there is no difference, I say there is but I've been known to be wrong. A surfactant is like a soap, matter of fact I've heard recommendations for non-ionic dish washing liquids like Joy being used. When added to the tank mix it breaks down the surface tension of the spray liquid when applied to foliage so it coats the foliage completely, not just bead up. A spreader/sticker is a surfactant with another ingredient such as an oil that helps the spray stay on the foliage after it is coated.