## Core Concept
Low birth weight is a critical parameter in neonatology and pediatrics, reflecting the health and development of newborns. It is defined based on the baby's weight at birth. The classification of birth weight is essential for identifying infants at higher risk for health and developmental issues.

## Why the Correct Answer is Right
The correct definition of low birth weight is less than 2,500 grams. This threshold is crucial because babies born with a weight below this are at an increased risk for various health complications, including respiratory distress, infections, and developmental delays. The World Health Organization (WHO) and other international health bodies recognize this cutoff.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify the correct weight threshold for defining low birth weight.
- **Option B:** Similarly, this option is incorrect as it does not accurately represent the definition of low birth weight.
- **Option D:** This option is also incorrect because it does not align with the established medical definition of low birth weight.

## Clinical Pearl / High-Yield Fact
A key point to remember is that low birth weight is a significant risk factor for neonatal morbidity and mortality. Babies with low birth weight may require special care and monitoring to manage potential complications. The definition of low birth weight as less than 2,500 grams is universally accepted and used in clinical practice for identifying at-risk infants.

## Correct Answer: C. Less than 2,500 grams.