Answer: Matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light
Dark matter is a type of matter, whose composition is unknown and which corresponds to 80% of the matter in the universe. Its name refers to the fact it does not emit or interact with any type of electromagnetic radiation, being completely transparent throughout the electromagnetic spectrum.
However, it interacts with the known matter through gravity.
This means that, like gravity, dark matter can not be observed directly, however its existence is inferred through the movement of the stars and the cosmic dust within the galaxies.