What are the differences between a zoo and a sanctuary?

Animal Sanctuary 

A facility that rescues and provides shelter and care for animals that have been abused, injured, abandoned or are otherwise in need, where the welfare of each individual animal is the primary consideration in all sanctuary actions. In addition, the facility should enforce a non-breeding policy and should replace animals only by way of rescue, confiscation or donation.

Zoo

All permanent establishments where animals of wild species are kept for exhibition to the public for seven or more days in a year, with the exception of circuses, pet shops and establishments which Member States exempt from the requirements of the Directive on the grounds that they do not exhibit a significant number of animals or species.

EU Zoos Directive

The difference?

The main difference between a zoo and a sanctuary is where the animals come from. A sanctuary doesn’t breed, doesn’t buy or sell, doesn’t exchange and for sure doesn’t trade with the animals! A sanctuary accommodates only those animals which can’t go back to their own natural habitat or wouldn’t survive being placed there. 
Often the animals are wild animals with physical or psychological  injuries, confiscated exotic pet animals, animals handed over or left by owners who couldn’t care or house the animals anymore (without danger), or animals confiscated or taken in after closing down of zoos, circuses, breeders or laboratories.
The sanctuaries safe those animals which cannot live in the wilderness and only survive when kept in confinement. They do there upmost best to provide a warm nest for each animal for the remainder of their lives.
Sanctuaries never use animals for entertainment of for shows just for the enjoyment of their visitors. Animal shelters and sanctuaries safe animals.

For more information: 

 

European Alliance of Rescue centres and Sanctuaries