Circumgalactic gas refers to the gas that surrounds and interacts with galaxies within their galactic halo. This gas plays a crucial role in the formation and evolution of galaxies, as it can affect the accretion of material onto galaxies, the fueling of star formation, and the feedback processes that regulate the growth of galaxies. Research in this area involves studying the properties and distribution of circumgalactic gas, as well as understanding its various interactions with galaxies. This includes measuring the temperature, density, and chemical composition of the gas, investigating the processes that drive gas inflows and outflows, and exploring the role of circumgalactic gas in shaping the overall structure and dynamics of galaxies. Overall, research on circumgalactic gas is important for gaining a comprehensive understanding of galaxy evolution and the complex interplay between galaxies and their surrounding environment.