A conversion funnel shows how many people move through a series of steps toward a goal. It is called a funnel because some people stop along the way, so fewer may reach each later step.
For example, a sign-up may begin with 1,000 visitors, then 620 start the form, 310 send their details, and 280 finish. Comparing the steps helps a team see where to investigate.
The numbers can mislead if steps are counted differently or tracking is broken. A funnel points to a place to ask questions; it does not explain by itself why people stopped.