**Core Concept**
DALY stands for Disability-Adjusted Life Year, which is a measure used to quantify the burden of disease in a population. It takes into account both the years of life lost due to premature mortality and the years lived with disability.

**Why the Correct Answer is Right**
A DALY is calculated by combining two components: Years of Life Lost (YLL) and Years Lived with Disability (YLD). YLL represents the number of years of life lost due to premature death, while YLD represents the number of years lived with a disability. The disability weights, which are used to quantify the severity of a particular health condition, are then applied to YLD to calculate the total DALY burden. This comprehensive approach allows for a more accurate assessment of the global health burden.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because Years of Life Lost (YLL) alone does not account for the years lived with disability, which is a critical component of the DALY measure.
**Option B:** Incorrect because Years Lived with Disability (YLD) alone does not account for the years of life lost due to premature mortality, which is another critical component of the DALY measure.
**Option C:** Incorrect because Disability-Adjusted Life Expectancy (DALE) is a different measure that estimates the number of years a person is expected to live in full health, rather than the total burden of disease.

**Clinical Pearl / High-Yield Fact**
The concept of DALY was first introduced in the 1990s as a way to quantify the global burden of disease and was later adopted by the World Health Organization (WHO) as a key metric for tracking progress towards health-related Sustainable Development Goals (SDGs).

**Correct Answer: D. Disability-Adjusted Life Year is a measure that combines Years of Life Lost (YLL) and Years Lived with Disability (YLD) to quantify the burden of disease.**