The way I explain the core is like a barrel.
You’ve got several layers of abdominal muscles and the deepest ones are the transverse abdominal belt, which is like a corset of muscles that wraps right around the torso.
If you think of this tightening like a belt or a corset, squeezing as tight as you can to 100%, these are your deep core muscles.
You can find these by poking your fingers side-on below your ribcage. Pressing quite firmly and giving a little cough.
You should feel those muscles the deeper muscles pushing back into your fingers. That is your transverse abdominal belt. Think of that as the outside edge of a barrel.
The lid of the barrel is your diaphragm, so as you breathe, the diaphragm pulls down to expand the lungs, and the base of the barrel is your pelvic floor, pulling up inside.
Now with a good connection through the pelvic floor, correct breathing practices, and that nice tight abdominal belt, you’re, that is your core.
The stronger your core, the better your posture, the better your balance, and the less pain that you’ll have.