SNP

A SNP (Single nucleotide polymorphism) refers to the most common type of genetic variation and is defined by a modification in a single nucleotide in a particular chromosome position (locus). Single nucleotide modifications can occur normally in the genome and it's common to find about 4-5 million single nucleotide modifications in a person's genome that have no impact in the  health or development of an individual.¹ However, when a single nucleotide modification is found at a specific position in over 1% of the population, it's officially considered a SNP.² 

 
SNPs can be found in coding and non-coding genome sequences. When found in a coding sequence (gene), multiple alleles in the single gene can result in a modified translated amino acid sequence. ²

The primary database for SNPs is dbSNP, maintained by the NIH.