* Matter is anything that has mass and takes up space.

Let's look at some common examples of matter and then consider what wouldn't fit:

* Solid: A rock, a piece of wood, a chair

* Liquid: Water, juice, oil

* Gas: Air, oxygen, carbon dioxide

Now, let's consider some things that are *not* matter:

* Light: Light has no mass and doesn't take up space. It's a form of energy.

* Sound: Sound is a vibration that travels through matter, but it's not matter itself.

* Thoughts: Thoughts are abstract concepts and don't have physical properties.

Therefore, the answer is light.