Matter has two major meanings: physical stuff and to be important.

In science, matter means anything that has mass and takes up space: the “stuff” the universe is made of. Rocks, water, air, your body, and the paper in a book are all matter. Matter can be solid, liquid, or gas, and it’s made of tiny particles like atoms and molecules. Even when you can’t see it easily, like the air in a room, it’s still matter because it’s physically real.

Matter can also mean to be important or to make a difference. If your teacher says, “Your effort matters,” she means it has real value and can change the outcome. If you tell someone, “You matter to me,” you’re saying they’re important in your life. People use this meaning when they ask, “Does it really matter?” They’re wondering whether something is worth caring about or whether it will actually affect anything.

A matter can also be a topic or problem that needs attention. For example, a legal matter is a legal problem you need to deal with, perhaps with the assistance of a lawyer.