The definition of a bridge page is simple.
You bring traffic to your page where you (normally) are trying to sell a product. If you have links from that page to an affiliate's page where they are also trying to sell the product, that's a bridge page. You cannot go from one sales page to another.
Think of it in the real world. You are shopping at a store and a salesperson comes along. Their job is to sell to you, make sure you go out of the store having bought something. They are very good at it and you tell them you will buy an item. You expect to be taken to the cash register, pay and get out. A bridge page would be if the salesperson says after you say you are ready to buy, "Great, talk to this other salesperson". You don't need to be sold to again, you've made your decision.
The solution to avoiding the bridge page policy is to bring them to your affiliate's checkout page, not their sales page.