The term "failure to thrive" has been used vaguely and in different contexts to refer to different issues in pediatric growth. It is most commonly used to describe a failure to gain weight, but some providers have also used it to describe a failure to grow, or a failure to grow and to gain weight. As used by pediatricians, it covers poor physical growth of any cause. The term has been used in different ways, and different objective standards have been defined. FTT is suggested by a fall in one or more weight centile spaces on a World Health Organization (WHO) growth chart depending on birth weight or when weight is below the 2nd percentile of weight for age irrespective of birth weight. In children whose birth weight was between the 9th and 91st percentile FTT is indicated by a drop across 2 or more centile spaces. Weight loss after birth is normal and most babies return to their birth weight by three weeks of age. Clinical assessment for FTT is recommended for babies who lose more than 10% of their birth weight or do not return to their birth weight after three weeks. Failure to thrive is not a disease, but a sign of inadequate nutrition.