The jaws are a pair of opposable articulated structures at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of humans and most animals.

The chelicerae are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or as a type of pincers. Some chelicerae, such as those found on nearly all spiders, are hollow and contain venom glands, used to inject venom into prey or a perceived threat. Both pseudoscorpions and harvestmen have additional structures on their chelicerae that are used for grooming. In Paratrechalea, males and females have shown to have a chelicerae dimorphism, because the chelicerae is used as a mating signal for females.