A polecat is a mustelid, a member of the weasel and badger family. "Polecat" is the common name of a number of species that all look roughly similar, although they live on different continents. In some parts of the United States, "polecat" refers to skunks rather to ferret-like wild animals.
The most well-known polecat species if the European polecat. These animals are the wild ancestors of the domestic ferret. Their bodies are much more weasel-like than cat-like, as they have small ears, long, low-slung bodies, and pointed muzzles. Like other polecats, they have a white head and a black, mask-like stripe over their eyes, just like domestic ferrets.
"Polecat" in the sense of a skunk may be due to the resemblance North American skunks have with the strikingly colored African polecat. African polecats are covered in horizontal black and white stripes, like many skunk species. Skunks are not true polecats or weasels, but they are not cats, either. They are their own group, the Mephitidae.