Description: Matter is anything that occupies space and has a mass. The most familiar states of matter are solid, liquid, gas, and plasma. The heating or cooling of a substance changes its state of matter from one form to another. The quantity of matter is measured in mass units, e.g. kilograms (kg).

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".