"Mass" is well defined. "Matter", less so. https://www.quora.com/What-is-the-difference-between-mass-and-matter-1 https://www.quora.com/What-is-the-difference-

"Mass" is well defined. "Matter", less so. https://www.quora.com/What-is-the-difference-between-mass-and-matter-1 https://www.quora.com/What-is-the-difference-between-mass-an...