A wasp's waist is called ...
Usually a wasp has three main body parts: the head, the thorax and the abdomen. Female one have stingers at the end of their abdomen. The gaster (the functional part of the wasp's abdomen) is separated with the thorax by the petiole. It's a narrow waist typical for bees, wasps and ants. The petiole may consists of one or two segments and this characteristic divides insects into two subfamilies. The petiole and the gaster form the metasoma together.