Bottom of the Funnel refers to a last stages of a sales funnel. When potential customers are in this phase they are aware of your brand and product, possibly researched it on their own, and are now almost ready to make a decision. Certain ads and content help them make this decision a little easier. Comparing the superiority of your product to the leading competitor, ebooks, white papers, customer reviews, and webinars are all ways to help push them to purchase your product or service.