An exoskeleton is an external skeleton that supports the body shape and protects the internal organs of an animal, in contrast to an internal endoskeleton which is enclosed under other soft tissues. Here are some key points about exoskeletons:

• Examples of exoskeletons in animals include the arthropod exoskeleton shared by arthropods (insects, chelicerates, myriapods, and crustaceans) and tardigrades, as well as the outer shell of certain sponges and the mollusk shell shared by snails, clams, tusk shells, chitons, and nautilus.
• Exoskeletons contain rigid and resistant components that fulfill a set of functional roles in many animals, including protection, excretion, sensing, support, feeding, and acting as a barrier against desiccation in terrestrial organisms.
• Exoskeletons have roles in defense from pests and predators and in providing an attachment framework for musculature.
• Exoskeletons, as hard parts of organisms, are greatly useful in assisting the preservation of organisms, whose soft parts usually rot before they can be fossilized.
• In addition to their natural occurrence in animals, exoskeletons have been developed as wearable devices for humans. A robotic exoskeleton is a mechanical device worn by a human being for certain purposes or applications. Exoskeletons are generally considered to be hard mechanical frames with joints that allow movement of the human operator. They can be used in the health sector and, in particular, in rehabilitation medicine, as well as in the military to reduce the physical burden on soldiers.

In summary, an exoskeleton is an external skeleton that provides support and protection to an animals body and internal organs. It can also serve other functional roles, such as defense and attachment for musculature. Exoskeletons can occur naturally in animals or can be developed as wearable devices for humans.