Before the 20th century, the term <answer>matter</answer> included ordinary <answer>matter</answer> composed of atoms and excluded other energy phenomena such as light or sound. This concept of <answer>matter</answer> may be generalized from atoms to include any objects having mass even when at rest, but this is ill-defined because an object's mass can arise from its (possibly massless) constituents' motion and interaction energies. Thus, <answer>matter</answer> does not have a universal definition, nor is it a fundamental concept in physics today. Matter is also used loosely as a general term for the substance that makes up all observable physical objects.
What term is used for the substance that composes all observable physical objects?
matter