A single-tail whip is any type of whip that has only a single tail, unlike, for example, a flogger, martinet or cat-o'-nine tails, which are all types of multi-tail whips.
A single-tail whip may have a stiff (e.g. wooden or metal) handle, or may be without a handle if its fat end is stiff enough by itself to be used like a handle.
Examples of singe-tail whips:
A short and stiff single-tail whip is close to a riding crop.
Illustration from the novel Maître et Esclave (1908).
Whip or crop?