Terms surrounding sudden infant deaths:

Apnea -- Episodes of cessation of breathing during sleep, either caused by some obstruction of the airway or for some unexplained reason. Often confused with SIDS, but there is no definite proof of a link.

Arousal response -- Awakening in response to environmental stimulation, from a loud noise to difficulty breathing. This response appears to be blocked or impaired in SIDS babies.

Autopsy -- A thorough pathological examination of a dead person, including examination of vital organs and lab analysis of blood and tissue to detect diseases, drugs or poisons in the system.

Bed sharing, also called co-sleeping -- When an infant shares the same sleep surface with another person, including parents or siblings. Investigators frequently decline to rule that a baby's death is due to SIDS when the infant was found in this setting, even absent evidence that another person in the bed rolled over on the child and caused crushing or suffocation.

Case history -- A careful review of written and verbal information about a baby's or the family's history of previous illnesses, symptoms, accidents, behaviors and other medical history.

Cyanosis -- Bluish discoloration of skin and mucous membranes due to lack of oxygen in the blood.

Death scene investigation -- Involves interviewing the parents and other caregivers and family members of a deceased infant about the location and condition of the child and other details, photographing and collecting items from the scene.

Home monitors -- Breathing monitors used to track infants at risk for apnea were once thought to hold promise in identifying babies at risk for SIDS, but research has not shown any advantage thus far, although a new generation of devices is being studied.

Mechanical suffocation -- Occurs when external pressure is applied to the body, preventing chest movement and breathing.

Petechiae (CQ)-- Small red spots on the skin or surface of an organ within the chest or abdominal cavity, produced by blood leaking from blood vessels. They are often found in the chest cavity of infants suspected to have died from SIDS.

Postneonatal -- The period of time in an infant's life after the first 28 days, and generally the period of risk for SIDS. Ninety percent of SIDS victims die before 6 months of age.

Prone sleeping -- Sleeping on the stomach, which increases the risk of SIDS by as much as 12-fold. Parents are urged to have their babies sleep supine, or on their backs, until they're 1 year old.

Rebreathing -- Breathing in exhaled air. Infants can experience excessive levels of carbon dioxide gas when they rebreathe air trapped in soft bedding.

Serotonin -- A hormone and brain-signaling chemical with multiple functions, but is known to have a role in regulating mood, emotion, sleep and appetite and is implicated in arousal and breathing. There is some evidence that a defect in a part of the brain that regulates breathing contributes to SIDS.

SIDS -- Sudden Infant Death Syndrome -- The third-leading cause of death among infants from 1 month to 1 year of age is diagnosed only when all other possible reasons for death, including trauma and illness, have been ruled out through an investigation and autopsy. The underlying physical causes of SIDS remain unknown.

SUID -- sudden unexplained infant death -- The death of an infant from no obvious cause. After investigation and an autopsy, about half of the approximately 4,000 sudden infant deaths in the United States each year are categorized as SIDS, the remainder as due to other undetermined circumstances, accidental suffocation or homicide.

Thermal stress, or overheating -- Thought to be a risk factor or contributor to SIDS, since being in a very warm room prompts babies to go into a deep sleep from which it is hard to wake up.

Triple risk model or theory -- Many researchers believe that SIDS happens in a confluence of several things at the same time. First, the baby has some congenital defect, perhaps in the brain stem, that makes him or her more vulnerable; be in a critical period of brain development, as babies are in the first year of life; and be exposed to some stress like secondhand smoke, an upper respiratory infection or sleeping on the stomach that would not alone cause death, but trigger the sudden shutdown of the body.