Single nucleotide polymorphisms (SNPs) are a type of polymorphism involving variation of a single base pair. Scientists are studying how single nucleotide polymorphisms, or SNPs (pronounced "snips"), in the human genome correlate with disease, drug response, and other phenotypes.
Single nucleotide polymorphism is way too many syllables, so you can understand why we just say "snip". And this is really a simple concept. These are the places in the genome where people differ. In about one out of every 1,000 letters of the code you'll run into one of these where I might have a C and you might have a T, and we'd call that a SNP. Most SNPs don't do very much, 'cause they're in a part of the genome that doesn't have a critical function. But some of them confer a risk of disease like diabetes or heart disease, and those are of intense current interest because of what they teach us about why those diseases happen.