The term "dark matter" is used to describe a hypothetical form of matter that does not interact with light or other forms of electromagnetic radiation. It does not emit, absorb, or reflect light, which is why it is considered "dark." The word "matter" is used because it refers to a substance that has mass and occupies space, even if it does not interact with light.
The name "dark matter" was coined by the astronomer Fritz Zwicky in the 1930s. He noticed that the visible matter in galaxy clusters was not sufficient to explain the observed gravitational effects. There appeared to be more mass present, which was not emitting any detectable electromagnetic radiation. This unknown form of matter came to be known as "dark matter."
Although the exact nature of dark matter is still unknown, it is widely accepted within the scientific community due to its gravitational effects on visible matter and the large-scale structure of the universe. Astronomers have observed its influence on the rotation of galaxies, the motion of galaxy clusters, and the bending of light in gravitational lensing.
While we may not fully understand the true nature of dark matter yet, the term "dark matter" is used as a descriptive placeholder until more is known about its composition and properties.