A marketing funnel, or marketing sales funnel, is a model for understanding the process of turning leads into customers. Like a funnel, marketers cast a broad net to drive brand awareness, capture as many leads as possible and then nurture prospective customers through the purchasing decision, which narrows in each stage of the funnel. The marketing funnel can be used to illustrate marketing effectiveness by measuring conversion rates between each step in the funnel, as a KPI.
A conversion funnel is really an idea or a way to visualize and comprehend the flow and conversion of potential customers into paying customers. If you can understand and analyze the process, then you can take actions to improve that flow.