What is MOFU? 

Second phase of the funnel or sales funnel, where potential buyers have already discovered what they want and move through the funnel to reach the middle part, where they value different options. At this stage, more specialized content should be offered, in exchange for the user submitting their data and becoming a lead. It consists of a more determined audience that has shown interest, so they have to show them the benefits of the product or service.

Other denominations:
Middle of the tunnel, second phase of the sales funnel