A skeleton is the hard structure that protects the internal organs of a living thing. Skeletons can be inside the body or outside the body. In mammals, which include humans, the skeleton is made of bones. All the bones, when they are joined together, make the "skeletal system" of a body. The skeletal system or "skeleton" is under the skin, the muscle and the tissue of the body. The skeleton supports the skin, muscle and tissue, and all the organs that are inside the body. The skeleton protects important internal organs like the brain, heart and lungs. If humans did not have a skeleton then the body would be flat as the skeleton gives the body its frame.

• Creatures that have skeletons inside their bodies are mammals, birds, reptiles and fish. A skeleton that is on the inside is called an endoskeleton.

• Some creatures, called arthropods, have skeletons outside their bodies. These are insects (like ants and bees), arachnids (spiders and scorpions), and crustaceans (sea creatures like crabs and lobsters). These creatures all have skeletons made of hard plates or shells. This kind of skeleton is called an exoskeleton
• A new born baby has 300 bones, but as they grow up to become an adult, their bones join together and the number lowers to 206 bones.