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 usually means a Labrador or Golden Retriever mix, or a dog with that look and unknown ancestry. Chesapeake Bay, Flat-Coated, Curly-Coated and Nova Scotia Duck Tolling Retrievers belong to the same family.
Most retriever-type dogs are medium to large, sturdy and food-motivated, with a water-resistant coat that sheds a good deal. Many are sociable and happiest carrying something in their mouths. A long, bouncy adolescence is common, and daily exercise and training help a lot. Ancestry varies, so meeting the dog tells you more than the label does.