Aculeata is a subclade of Hymenoptera. The name is a reference to the defining feature of the group, which is the modification of the ovipositor into a stinger (thus, the group could be called "stinging wasps", though the group also contains the ants and the bees). In other words, the structure that was originally used to lay eggs is modified instead to deliver venom. Not all members of the group can sting; a great many cannot, either because the ovipositor is modified in a different manner (such as for laying eggs in crevices), or because it is lost altogether.