Terrier is a label for a whole family of earth dogs, from Jack Russells and Rat Terriers to Cairns and Yorkies, developed over several centuries to chase rats and foxes into burrows. On adoption listings it usually means a small to medium dog, often a mix, with a wiry or smooth coat and a weight somewhere between 10 and 35 pounds.
Most are affectionate, loyal and full of opinions. Digging, barking and chasing squirrels are common habits, and Ann Arbor's tree-lined streets and parks supply plenty of squirrels to chase. Because ancestry is often a guess, a dog's size, coat and energy are better read from how it behaves than from the label. Plan on daily exercise, a secure fence if you have a yard, and patient, reward-based training.