Retriever is a type of gun dog rather than a single breed. The label covers dogs developed to find shot birds and carry them back to the hunter gently, and on adoption listings it most often means a Labrador or Golden Retriever mix, or a dog with that look whose exact ancestry is unknown. Chesapeake Bay, Flat-Coated, Curly-Coated and Nova Scotia Duck Tolling Retrievers belong to the same family.
Most retriever-type dogs adopters meet are medium to large, sturdy and food-motivated, with a water-resistant coat that sheds a good deal. Many are sociable, eager to work with people and happiest carrying something in their mouths. They usually need daily exercise and training to channel that energy, and a long, bouncy adolescence is common. Because ancestry varies, the shelter's notes and a meeting tell you more than the label.