The term 'CAVITIES IN BODY' can be summarized by the crossword solution 'ANTRA', which stands for 'anatomical term for cavities in the body'. Anatomical terms are used to describe the structure and function of the human body, and 'antra' is a term used to refer to the hollow spaces or cavities found in the body. These cavities can contain organs, such as the heart, lungs, and stomach, and can also be filled with air or fluid.