In the real world, we are introduced to brands, products, and/or solutions in various ways. On TV, on a billboard while driving, word of mouth, in a store, or while window shopping on the web. Attribution refers to how marketers credit the proper source, one of many marketing channels, to an outcome. An outcome being a sale or any type of conversion you sought to achieve as a goal. You might want to check out what an attribution model is, and the various models you could possibly use.