Copy number variation (CNV) refers to a type of genetic variation where sections of the DNA are duplicated or deleted, resulting in an abnormal number of copies of certain genes. CNVs can have a significant impact on an individual's phenotype, as they can affect gene expression levels and lead to a variety of diseases and disorders. Research in this area focuses on identifying CNVs, understanding their impact on human health, and developing methods for detection and analysis of CNVs. This field has important implications for understanding the genetic basis of diseases and developing personalized medicine approaches.