What is the invisible substance that makes up to 21 percent of the universe?

The invisible substance that makes up about 21 percent of the universe is known as dark matter. Unlike ordinary matter, dark matter does not emit, absorb, or reflect light, making it undetectable by conventional means. Its presence is inferred from gravitational effects on visible matter, such as galaxies and galaxy clusters. Dark matter plays a crucial role in the structure and evolution of the universe.