Microsatellite instability (MSI) is a term used to describe the repetitive DNA sequences within a genome that have a tendency to expand or contract. MSI can lead to a range of genetic disorders, including cancer and neurological diseases. Some synonyms that are commonly used to describe MSI include mini- and short tandem repeats (STRs), simple sequence repeats (SSRs), and microsatellite variation. These terms refer to similar genetic phenomena where small nucleotide sequences are subject to variations that can have profound effects on gene expression and regulation. Researchers and clinicians use these terms interchangeably when investigating the causes and pathogenesis of diseases associated with MSI.