Human mitochondrial DNA haplogroup
Mitochondria are the primary energy generator of the cell and have unique organelles that maintain their own DNA (mtDNA). In human genetics, human mitochondrial DNA haplogroups are collections of similar haplotypes defined by combinations of single nuclear polymorphism (SNPs) in mtDNA inherited from a common ancestor.
Source: Wikipedia — Human mitochondrial DNA haplogroup (CC BY-SA 4.0)