What is matter?
Matter is anything that has mass and takes up space.
Mass is what gives things weight on Earth. If something feels heavy, it is matter. But the helium in a balloon is also matter. It only floats because air is heavier.
Most of the matter we encounter every day is made up of atoms. Your body, the ground under your feet, the air you breath, are all made of atoms.
Inside the atoms, there are protons and neutrons in the nucleus, and electrons in clouds around the nucleus. All of these particles have mass and take up space.
Protons and neutrons are in turn made up of even smaller particles, called quarks. And there is a whole zoo of particles that we see when we smash atoms together, with names like muons, taus, and neutrinos.
There are also things that aren’t matter. These are called particles, but they have no mass and they take up no space. They carry force, and matter reacts to these forces. The photon carries the electromagnetic force, and allows us to see, to feel heat, to send radio signals, and take X-ray pictures. Other force carrying particles are bosons and gluons.
We also suspect that there is a lot of matter in the universe that we cannot see. We call it dark matter, and it is responsible for keeping galaxies from flying apart. It may be made up of particles that we have not yet detected. Some of it is undoubtedly neutrinos and black holes, but there seems to be far too much of it to be made up of just those things we know about.