The intergalactic medium (IGM) is the diffuse gas and plasma that fills the vast spaces between galaxies in the universe. It consists of mostly hydrogen and helium gas, as well as trace amounts of other elements. Researchers study the IGM to understand the processes of cosmic evolution, such as the formation and evolution of galaxies and the distribution of matter in the universe. Observations of the IGM can provide insights into the physical conditions of the early universe, the process of cosmic reionization, and the interplay between galaxies and their surrounding environment.