So, endoskeleton literally means "inner skeleton". Humans have an endoskeleton because their skeleton is located *within* their bodies, supporting them from the inside.
Here are some other words that use the root "endo-":
* Endocrine: Relating to glands that secrete hormones directly into the bloodstream (within the body).
* Endoderm: The innermost layer of cells in an embryo.
* Endometrium: The inner lining of the uterus.
* Endothermic: An organism that can maintain a stable internal temperature (heat generated from within).