Exclusive casino bonuses are offers available only for certain customers or on certain occasions. They are not for everyone, as the name suggests.
Exclusive casino bonuses might include some VIP promos like higher cashback, more advantageous bonus terms, or simply bigger bonuses overall. As a rule, you need to be a VIP member to receive them.
Likewise, they can be just themed promo offers like Christmas, Halloween, or New Year bonuses and bonuses for newly-released casino games.