Galaxy overdensity refers to regions of space that have a higher than average concentration of galaxies compared to the surrounding space. Such regions are usually identified through surveys of large areas of the sky, where clusters or groups of galaxies can be detected based on their clustering patterns and distances. Studying galaxy overdensities can provide insights into the large-scale structure of the universe, the formation and evolution of galaxies, as well as the effects of dark matter and dark energy on the distribution of matter in the cosmos. This area of research is crucial for understanding the overall structure and dynamics of the universe.