When you're at another person's house, the place that they prefer to sit. This place is usually the most comfortable seat in the whole room, and near and dear to the host's heart. The host is usually very reluctant to give somebody permission to sit there, and often takes offense to those who sit there with out asking.
Often used in 3rd person
Host: Dude, get up!!
Host: That's Papa Bear's Chair!
Guest: My bad, i'm sorry...