What does it mean to have failure to thrive?

Pediatric Undernu- trition, characterized by weight-for-length or BMI of < 5th %ile, is defined as "an imbalance between nutrient requirements & intake that results in cumulative deficits of energy, protein or micronutrients that may negatively affect growth, development & other relevant outcomes." Causes of PUN can be prenatal exposures, genetic disorders, physical illnesses &/or environmental/behavioral factors.
Not growing properly. Failure to thrive is when an infant is not growing as expected in comparison to the norms. There are groth charts which are based upon the norms and those that are falling off the normal growth curves are considered failure to thrive. This terminology is more common in infants but can be used in older children.