Backbone/ˈbækbəʊn/ Definition 1 of 3Pro Tip 1/2Physical Structure Refers to the actual bones within the body, often mentioned in medical or injury contexts. The X-ray showed she had fractured her backbone. Pro Tip 2/2Not The Surface Used to talk about the inner structure, not external back muscles or skin. Old age can lead to issues with one's backbone due to osteoporosis.