The "Championship Belt" concept comes from boxing/wresting and is the idea that every season, the previous years champion (here the Super Bowl) starts with the belt, and each time they lose they pass the belt to the winning team who becomes the new sole owner. 

https://grantland.com/the-triangle/introducing-the-nba-regular-season-championship-belt/

currently hold the championship belt having defeated the Chiefs in Week 11.

Week 13: Bills attempt to defend against 49ers

This market closes at the conclusion of the regular season, resolving simply with the team who holds the belt after Week 18. I'll update each week with the current owner of the belt. As a fun edge case, a tie would resolve in a division into two different belts (and could resolve for multiple teams).