An Exclusive means a knife made exclusively for a distributor, dealer, or forum. The knife is only made available through whatever channels said party chooses, and is not available through the Spyderco Online Store. The only exception is for those collector's club members who participate in the appropriate level that guarantees them each permutation of every knife. Unlike a sprint run, which has a set quantity made, an exclusive often has the option to have subsequent quantities produced.
Usually that means that the distributor has ordered a whole run of a particular knife made to their specifications. This usually involves some sort of modification to handle color/materials and blade steel selection. It may also involve custom engraving on the blade, such as a forum logo.