Exclusive offers are ones that only a few to one affiliates have that you can't find no where. They either deal directly with the company or make out a special deal with an affiliate. Normal offers are something that all affiliates have, exclusive offers are the ones that only a few affiliates have.
Most networks will allow you to decide which affiliates get what. While you might want to give all affiliates for example a 15% coupon to your site, one big affiliate might get a 20% coupon which is exclusive to them. This is an important practice in affiliate marketing. Its a good way to make affiliates feel that they are special and different from the rest.