Terrier is a label for dogs developed over several centuries, mostly in Britain, to hunt vermin, often by going underground after them. On adoption listings the word usually describes a small to medium mix with terrier looks rather than a single known breed, typically 10 to 35 pounds, with a wiry or smooth coat.
That background shows up in everyday life. Terriers tend to be alert, bold and loyal, with a habit of barking at passersby and digging in loose dirt. Many do well with a secure yard and a shaded spot to rest. A dog's actual size, coat and energy depend on its ancestry and age, and many live 12 to 16 years, so adopting one is a long commitment.