riding crop
A short, semi-rigid whip without a lash. Normally used for horse riding, but nowadays more often associated with BDSM.
Riding crops are often confused with teachers' pointers. A riding crop usually has some flex to it and often widens and flattens into a rectangular shape at its very tip. Pointers are usually thinner, completely rigid and may have an oblong cushion on the end. Even artists sometimes conflate the two.