Genome size refers to the total amount of genetic material, or DNA, contained within an organism's cells. It can vary greatly between different species, from the relatively small genomes of bacteria and viruses to the much larger genomes of complex organisms like humans. Genome size is influenced by factors such as the number of genes, amount of non-coding DNA, and presence of repetitive sequences. Researchers study genome size to better understand the organization and function of genetic material, as well as to explore the evolutionary relationships between different species. Techniques such as genome sequencing and comparative genomics are used to analyze and compare genome sizes across a wide range of organisms.