How do scientists define matter?
Matter is anything that has mass and takes up space (has volume).
Matter is composed of atoms containing protons, neutrons, and electrons. Matter has physical and chemical properties, such as boiling point (physical) and flammability (chemical). Matter can be invisible to the naked eye, such as the gases that make up the atmosphere. Matter can also be visible which makes up so much of our physical environment that we can observe or touch with our senses. Aside from the gases in the atmosphere, most of our world is composed of visible matter, such as grass, shoes, desks, trees, water, paper, pens, pencils, roads, cars, airplanes, etc.
What matter is not, is energy. This includes heat, and all forms of electromagnetic radiation.