A sales funnel is a set of invisible steps you lay before visitors that takes them from the point of entry to the desired action. There are three stages in a sales funnel:
Top of the funnel (TOF), Middle of the funnel (MOF), Bottom of the funnel (BOF). Why do we call these three stages a funnel? Because, together, they form a funnel-like shape:
A sales funnel and its three key stages: top-of-funnel, middle-of-funnel, bottom-of-funnel marketing.
https://www.smashingmagazine.com/2019/12/design-profitable-sales-funnels-mobile/