Programmed cell death: a regulated, energy-dependent process by which a cell dismantles itself in orderly stages, condensing, fragmenting, and being cleared away so the larger organism may live and remain shaped. Where necrosis is chaotic death by injury, apoptosis is death as design.

From Greek apóptōsis "a falling off," from apo- "away" + piptein "to fall." The modern scientific term was introduced in the 20th century to name a process long observed but newly understood, the body's quiet art of subtraction.