Final answer:
Dark matter is the non-luminous material that is inferred to exist due to its gravitational effects on visible matter, radiation, and the structure of the universe, constituting about 90% of the universe's total matter.
Step-by-step explanation:
The matter that we infer to exist from its gravitational effects but from which we have not detected any light is called dark matter. Dark matter is significant because it is believed to constitute approximately 90% of all matter in the universe. Its presence is implied by observable gravitational effects on visible matter, radiation, and the large-scale structure of the universe, yet it remains undetected by electromagnetically based observational instruments. We witness these gravitational effects in phenomena such as the bending of light from distant galaxies, an effect known as gravitational lensing. However, the exact nature of dark matter is one of the most pressing problems in physics today, as it could imply entirely new realms of physics or even undiscovered particles.