A single-nucleotide polymorphism (SNP) is sequence variation at the single-base level. They can be found in coding, non-coding, and intronic regions of genomes, and they may affect transcription factor binding, gene splicing, protein folding, and many other elements at the gene and transcript level.
SNP variations in the human genome are believed to be associated with diseases and malignancies. Many linkage and association studies have been performed to connect allelic variation to diseases. There are currently more than 50+ million SNPs listed by dbSNP (NCBI) in the human genome, trending 2-3 million new discoveries every year.