Cold dark matter (CDM) is a theoretical form of matter that does not emit, absorb, or reflect light, making it invisible to telescopes. It is believed to make up about 27% of the universe's total mass and energy. CDM interacts primarily through gravity, influencing the formation and structure of galaxies and galaxy clusters. Scientists propose that CDM consists of slow-moving particles, which allows it to clump together under the influence of gravity. This clumping is essential for the formation of large-scale structures in the universe, such as galaxies and galaxy clusters, providing a framework for understanding cosmic evolution.