A funnel in the context of customer relationships refers to a model that illustrates the journey potential customers take from the initial awareness of a product or service to the final stage of making a purchase. It is typically visualized as a funnel because it starts with a broad audience at the top and narrows down to those who convert into paying customers at the bottom. The funnel is used to understand and optimize each stage of this journey, which includes awareness, interest, consideration, and decision-making.