From Brickipedia, the LEGO Wiki
Exclusives is a special line that targets adults aged 12 and above. Exclusives (typically with more than 1000 pieces) are often available only at the LEGO Shops or at LEGO Stores. Key chains and magnets with minifigures are also considered as exclusives as they are only available at the LEGO Shop.
The largest exclusive is the 10189 Taj Mahal. Both Star Wars, DC Universe Super Heroes, and Harry Potter have released licensed exclusives.