I explain it as the bridge of support from the lower body to the upper body, or as the core cylinder.
I also use the term, “core cylinder,” to give clients the connection to the pelvic floor, the diaphragm, and the entire team of muscles and fascia that supportive torso along the front, back, and sides.
The core to me are all the muscles and connective tissues that stabilize the body so that the arms and legs (and sometimes neck) can function as we need them to do. These muscles also stabilize the spine in order to do this and to maintain the integrity and health of the spine.
I teach a CEC series on the integration of stability and core development. Check out my website at www.hawaiifitnessacademy.com sometime.
Joanne, you already know the answer to this question. Core is abs and lower paraspinals, obliques, transverse ab. One of the best exercises is lying prone, simply do a back extension, no movement at hips or legs, go to about 25-30 degrees of extension. Keep the neck in neutral throughout, no extension.
Id describe it as area above and around the hips and below the chest.
It helps stabilize the body when standing, provides internal pressure to create strength, protects internal organs, and creates a fluid motion when in movement.
The last part is especially important when telling clients not to use the handlebars on treadmills or elliptical in order to keep it a full body movement.