In dog-speak, a tail’s “root” is where it sets into a dog’s body.

A tail that is thick and covered with hair at the “root” for several inches, then tapers to a fine point where the hair looks as it’s been shaved is known as a “rat tail.”  A rat tail is a hallmark of the Irish Water Spaniel, but definitely not in a Treeing Walker Coonhound where it’s a fault (from its breed standard: “Fault – having an excess of curve in tail; rat tail; excessive brush), or in the American Foxhound (“Defect: A long tail, teapot curve or inclined forward from the root. Rat tail, entire absence of brush”).

Irish Water Spaniel by Edwin Megargee (1883 -1958 )