A single nucleotide polymorphism (SNP) is a variation at a single position in a DNA sequence among individuals. For example, in a specific region of the genome, one person might have an adenine (A) while another has a guanine (G). These small changes can influence how genes function and contribute to differences in traits, such as susceptibility to diseases. SNPs are the most common type of genetic variation in humans and can be found throughout the genome. They are important for genetic research and can help scientists understand the genetic basis of diseases, as well as how individuals respond to medications and environmental factors.