A good explanation of Guaranteed vs remnant advertising. In a direct or Guaranteed campaign you pay a premium and are guaranteed the number of impressions and in a remnant market, you get the inventory that is not sold.
Roadblock Advertising allows advertisers to own 100% of voice for a given period, usually a day. In other words, an advertising campaign would run exclusively across all the advertising units on a page reinforcing the advertising message. Ideal for a brand or product launch when the aim is to gain brand awareness quickly.
Remainder advertising (also known as remnant or last minute advertising) refers to the advertising space that a media company has been unable to sell. Depending on the medium, it could be ad space or time. Often it can be bought at a steep discount. Advertising time and space is a perishable commodity. If it is not sold, it is lost, used for a "house ad", or given away for public service announcements or some other non-revenue producing filler.
A leaderboard is a popular type of banner advertisement. At standard dimensions of 780 X 90 pixels, a leaderboard is the width of the page and typically lies between the masthead (the title area at the top of a Web page) and content.
If you are a content producer or a freemium app or game developer, you would know, instantly, what I am talking about: there is WAY too much ad inventory out there. Too many eyeballs that are not getting adequately monetized. Major publishers sitting on top of huge masses of unmonetized impressions. Game developers monetizing, barely, 1-2% of their traffic. App developers, similarly, struggling to convert free users to premium.