SNP stands for Single Nucleotide Polymorphism, a location in the genome that is known to differ between individuals. The rs number is used by researchers and databases to refer to specific SNPs.
SNPs normally occur throughout a person's DNA, almost once in every 1,000 letters (A, T, G, and C) on average.
Most SNPs don't have a critical function and thus do not affect health or development. But some of them confer a risk of diseases like diabetes or heart disease. These SNPs are of current interest to researchers because they give insights into why those diseases happen.
Researchers have found that SNPs also influence an individual's response to certain drugs and susceptibility to environmental factors such as toxins and allergens. SNPs are also used as "markers" or indicators to track the inheritance of disease genes within families.