| Asteroid | A celestial body composed of rocks, metals and sometimes ice that remains after the formation of the planets. |
| Atom | An element of matter composed of a nucleus and electrons. It can combine with other atoms to form molecules: the water molecule is the combination of one oxygen atom and two hydrogen atoms. |
| Cell | Smallest living unit capable of autonomy and reproduction. |
| Comet | A celestial body composed of ice and dust that remains after the formation of the planets. |
| Continent | In geology, a large block of continental crust, composed mainly of silica-rich rocks such as granite. From this point of view, today's Europe and Asia would be considered as a single continent. |
| Earth's magnetic field | The force field protecting Earth from solar wind particles. It is generated by Earth's liquid outer core, which creates electrical currents and steers our compasses. |
| Elementary particles | Small particles that make up matter. Current physics considers that they are not themselves made up of smaller particles. |
| Fossil | Trace of an ancient living being preserved in sedimentary rock. |
| Fusion | Energy-producing reaction in which atomic nuclei join together to form a heavier nucleus. |
| Galaxy | A cluster of gas, dust, stars and their planets, often with a massive black hole at its centre. |
| Genome | All the material containing an individual's genetic information encoded in the DNA molecule. It takes the form of one or more chromosomes, depending on the species. |
| Gravity | Force that attracts all objects with mass together. |
| Light | Visible light, made up of the colours of the rainbow, is just one type of electromagnetic radiation. The electromagnetic spectrum also includes gamma rays, X-rays, ultraviolet rays, infrared rays and radio waves. |
| Light-year | Unit of length used in astronomy, equivalent to the distance travelled by light in one year, i.e., approximately 10,000 billion kilometres. In one second, light travels 300,000 km. |
| Nucleic acid | Carrier of the genetic information that determines the biological identity of every living being. |
| Oxidation | A chemical reaction, often caused by oxygen, in which an atom or molecule loses electrons. |
| Plate tectonics | A scientific model describing Earth's crust and upper mantle as being divided into plates that are constantly moving relatively to each other like conveyor belts. |
| Protein | Chain of linked amino acids. They perform essential functions in living cells: chemical reactions, structure, carrying information, etc. |
| Satellite | A natural or artificial object that orbits a planet due to its gravitational attraction. |
| Silicate | A crystalline mineral composed mainly of silica and oxygen. |