**Core Concept**
The World Health Organization (WHO) defines health as a state of complete physical, mental, and social well-being, and not merely the absence of disease or infirmity. This definition emphasizes the importance of physical, mental, and social aspects of health.

**Why the Correct Answer is Right**
The WHO definition of health has been widely accepted and is the foundation for global health policies. However, some argue that the definition should include the concept of "environmental well-being." Environmental well-being encompasses the impact of environmental factors on human health, including pollution, climate change, and access to clean water and sanitation. This component is essential for understanding the complex relationships between human health and the environment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because "spiritual well-being" is not explicitly mentioned in the WHO definition of health. While spiritual well-being is an important aspect of overall health, it is not a component of the WHO definition.

**Option B:** This option is incorrect because "occupational well-being" is not a recognized component of the WHO definition of health. While occupational health is an important aspect of public health, it is not a standalone component of the definition.

**Option C:** This option is incorrect because "genetic well-being" is not a distinct component of the WHO definition of health. While genetic factors can impact health, they are not a separate aspect of the definition.

**Clinical Pearl / High-Yield Fact**
The WHO definition of health has been influential in shaping global health policies, but it has also been criticized for being too broad and lacking specificity. Understanding the limitations of this definition is essential for healthcare professionals working in global health.

**Correct Answer: D. Environmental well-being.**