When a client buys an article or video or another piece of content on Collegehumor.com, they have the option of purchasing advertising around that content. Since the content is created by the CollegeHumor staff, there is an 80:20 ratio that is implied in terms of branding; 80% CollegeHumor, 20% Client. This feels less like advertising to users, and more like an informative graphic letting them now that there's a new item on the site for them to check out.
When there are Cobrand units, they usually come in multiple forms including Site Skins, Billboard Banners, Leaderboard Banners and even a couple of units that are exclusively run on CollegeHumor.