A sales funnel is a marketing concept about making a sale in a business. The word funnel is used because of its shape of going from a large opening to a small opening. Typically, many people might show some interest in your product or service but only a few actually purchase.
This process can be described in series of steps of awareness, evaluation and conversion. The top of the sales funnel is to raise awareness for your product or service. People then evaluate your product or service but this is less people than became aware of it. The third step is conversion where some of the people who evaluated your product or service convert to actually purchasing it.