An infant whose weight at birth is less than 1500 grams (3.3 lbs), regardless of gestational age. The trait is very low birth weight infant (Experimental Factor Ontology term EFO_0003965). Also known as: INFANT VLBW, Infant, Very Low Birth Weight, Infant, Very-Low-Birth-Weight, Infants, Very-Low-Birth-Weight, VLBW INFANT, Very Low Birth Weight, Very Low Birth Weight Infant, Very-Low-Birth-Weight Infant.