A funnel is a physical pipe that is wide at the top and narrow at the bottom.
A marketing and sales funnel or purchase funnel is a metaphorical pipe that illustrates how prospects at the top are filtered to customers at the bottom.
As it is wide at the top and narrow at the bottom, there are more prospects than customers.
In the marketing and sales industry that term, funnel is used a lot.
E. St. Elmo Lewis who created AIDA, came up with this.
I think it is a bite erroneous.
A marketing and sales pipeline is more useful.
A pipeline is a series of pipes, often underground, with pumps and valves for flow control, used to transport liquid and gas over great distances.
A marketing and sales pipeline is a metaphorical series of funnels with flow control that illustrates how prospects are transported over great distances to become customers.
When you look at customer journey it is never as simple and linear as a funnel.