A Sales tunnel (also called a Sales pipeline, or a Sales funnel to emphasise the volumetric changes in deals) is the way that both direct sales persons and SFA systems visualise the sales process of a company. In any step of the sales process prospects drop out of it, and from the large number of initially interested persons on the narrow end of orders only a fraction of the initially interested people remain and actually place an order. The structure may start at various process steps (e.g. a sales lead, or later, a sales offer) to a closed/finished contract or Deal Transaction.
A sales funnel is constructed by stacking several layers together. Typical layers include:
New opportunities are put in the top and worked through the funnel until they either issue a purchase order, or become a disqualified lead. The key to surviving in sales is to make sure that each layer never goes empty. You should always know how many companies are in each layer. The adage is "Fat pipeline equals skinny kids." One-call closers have fat kids with better toys.
Knowing that it can take weeks or months to walk prospects through the funnel process, you better have multiple prospects at all the layers of the funnel.
So the bottom line is pretty straightforward. Make sure that you have action at all levels in the sales funnel and you'll never be desperate for a deal to close again.