any of a breed of hardy pony (typically 38-40 in, 96.5-101.5 cm, in height), originally from the Shetland Islands, with a full mane and tail and a shaggy coat in winter
See Shetland pony in American Heritage Dictionary 4
noun
A small, compactly built pony of a breed originating in the Shetland Islands, having a long thick mane and tail.