A marketing funnel is the deliberate system you build to move strangers from awareness to purchase. Three stages: TOFU (Top of Funnel — awareness, blog posts, social content, paid reach), MOFU (Middle — consideration, email nurturing, case studies, retargeting, lead magnets), BOFU (Bottom — conversion, demos, consultations, direct offers). Most small business funnels break at MOFU — they get visitors and can close when talking to prospects, but have no system to stay in front of warm leads between first contact and purchase. Email nurturing is the most reliable MOFU fix. Build the list, send it value, let time and trust do the work.