Anything mitochondrial has to do with the tiny energy-producing organelles in a cell. Mitochondrial diseases result in damage to cells when they can't generate enough energy.
Mitochondrial comes from mitochondria, those billions and billions of minuscule parts of a cell that act as its battery, generating energy to keep it functioning. A German microbiologist coined the word from Greek roots mitos, "thread," and khondrion, "little granule." Mitochondrial DNA is the specific genetic material within mitochondria; and mitochondrial therapies can involve replacing parts of a person's mitochondria in order to treat or prevent certain diseases.