Exclusive weapons are guns, grenades or melee weapons that do not exist in the real world. Typically such weapons are just cosmetic variants of an existing gun already in the game, but it can occasionally be a completely new weapon not specifically based on another (for example, the Plasma Gun).
Sometimes, A.V.A will base a weapon off a similar entity in a different game (such as the Holy Mackerel), but as long as the weapon meets these criteria, it still falls under the Exclusive category.
The majority of capsule weapons are Exclusive, but again, there are a few exceptions such as the Super Redhawk. Dual wielded weapons (Dual Uzi, Dual TMP, etc.) are not considered Exclusive if their singular variant has not originated from A.V.A. All cosmetic variants of weapons are taken to be Exclusive.