Apparent life-threatening event (ALTE): sudden event, frightening to the observer, in which the infant exhibits a combination of symptoms, including apnea, change in color (pallor, redness, cyanosis, plethora), change in muscle tone (floppiness, rigidity), choking, gagging, or coughing

Apnea: cessation of respiratory airflow for any reason; central, obstructive, or mixed

Pathologic apnea: apnea lasting 20 seconds or more and accompanied by bradycardia, cyanosis, hypotonia, or other signs of compromise

Apnea of infancy: unexplained respiratory pauses lasting 20 seconds or more, or pauses of less than 20 seconds that are accompanied by pallor, cyanosis, bradycardia, or hypotonia in the term infant; this term is reserved for infants with ALTE in whom no plausible etiology is identified.

Apnea of prematurity: pathologic apnea associated with preterm delivery; usually resolves by 37 weeks’ gestation but may continue several weeks beyond term

Periodic breathing: breathing pattern in which three or more pauses occur, each lasting more than 3 seconds, with less than 20 seconds of normal respiration between pauses

Sudden infant death syndrome: sudden death in a child without historical, physical, laboratory, or thorough postmortem findings that explain the cause of death