**Core Concept**
The deficit in weight for height in a 3-year-old child is an indicator of acute malnutrition, which occurs when the child's weight is below the expected weight for their height. This condition can be caused by inadequate nutrition, chronic illness, or other underlying factors.

**Why the Correct Answer is Right**
The weight for height index is a sensitive indicator of acute malnutrition because it takes into account the child's current weight relative to their height. A deficit in weight for height indicates that the child has lost weight over time, which can be a sign of an underlying issue such as infection, inflammation, or inadequate nutrition. In a 3-year-old child, this deficit is particularly concerning as it can impair growth and development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the concept of weight for height deficit.

**Option B:** While stunting is a type of malnutrition, it refers to a deficit in height for age, not weight for height.

**Option C:** This option is not a direct indicator of acute malnutrition.

**Clinical Pearl / High-Yield Fact**
A child with a deficit in weight for height is at increased risk of complications such as impaired growth, weakened immune system, and increased susceptibility to infections.

**Correct Answer:** D.