What do we mean by body mass, or, more specifically, the word mass? Mass simply means "substance" and "matter." If an object has substance and occupies space it has mass. What's more important, if it has mass it can attract and pull on other objects that have mass too. Athletes are made up of muscles, bones, fat, tissues, and fluids, all of which are substance pr matter and have mass. So an athlete, having mass, pulls on the earth, and the earth, having madd as well, pulls on the athlete.