A martinet is a short, scourge-like (multi-tail) type of whip made of a wooden handle of about 25 cm (10 inches) in length and about 10 lashes of equal, relatively short length. The lashes are usually made of leather, but sometimes soap-stiffened cords are used in place of leather. It is a traditional instrument of physical punishment in France (in French it also meant a similar dusting implement; the type for chastisement was also known as fouet d'enfant, 'child's whip') and other European countries.
The martinet was often applied on the calves, for children did not have to disrobe that way. Otherwise it was often applied on the bare buttocks, adding a dose of humiliation to the physical pain, like the English and Commonwealth caning, birching, naval boy's pussy, American paddling, et cetera. As it is not blunt or heavy impact on clothes would be reduced too much to remain effective.
It is generally considered abusive to use it for spanking children in modern times. Still, martinets were still sold in the pet section of French supermarkets; it is generally believed that a large share of those sold are meant for use on children, not pets, or at least to threaten them. But nowadays many supermarkets in France have stopped selling the martinet even in the pet section. It is also often still carried demonstratively by Zwarte Pieten (male black assistants of Saint Nicholas, the European original of Santa Claus, celebrated on December 6; attribute persisting where lashes are banned, as in Belgium) to chastise very naughty kids instead of leaving presents.