Really? In all simplicity it's the understanding that at their most basic levels energy and matter have similar expressions and in some cases they can be indistinguishable one from another. It's also the understanding that the 'rules' of the universe we can physically observe (motion, gravity, inertia, heat, cold, etc.) don't necessarily apply to all states of energy or matter. Which some people would call quantum mechanics.
In microcosm I enjoy how you can observe quantum state interactions in real life. Like when you make tapioca pudding and as it cooks there's this split second where it suddenly transforms from a liquid into a viscous state and then as it cools it can become semi-solid.
Tapioca also forms in 2mm to 6mm slabs or sheets analogous to how some people view some forms of quantum strings as sheets. My impressions are that the similarities are not coincidental.
So in cooking a simple dessert you can observe expressions of both chemical bonding and the covalent bonding that occurs within the chemical bonding.