Apoptosis
describes the molecular and morphological changes that characterize controlled cellular self-destruction, often called "programmed cell death".
defined: Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.
explained:
Listen to a detailed explanation. Dr. Jennifer Puck, of the National Human Genome Research Institute's Genetics and Molecular Biology Branch, defines apoptosis.
related terms: 
cell
The genetically programmed death of cells at specific times during embryogenesis, metamorphosis, and during cell turnover in adults.