any of various very small, usually rodlike structures found in the cytoplasm of eukaryotic cells and that serve as a center of intracellular enzyme activity which produces the ATP needed to power the cell
See mitochondrion in American Heritage Dictionary 4
(mīˌtə-kŏnˈdrē-ən)
nounpl.mi·to·chon·dri·a(-drē-ə)
A spherical or elongated organelle in the cytoplasm of nearly all eukaryotic cells, containing genetic material and many enzymes important for cell metabolism, including those responsible for the conversion of food to usable energy. Also called chondriosome.