What is a condition where the body is unable to function properly called?

The term that best describes a situation where the body is unable to function properly is "disease." In a medical context, a disease refers to a pathological condition of a bodily part, an infection, or other system that disrupts normal bodily functions. This may include various forms of infections, chronic illnesses, and disorders that lead to a decline in health or ability.

In contrast, an injury typically refers to a physical harm or damage to the body, which may not involve a disease process. The term "condition" is quite broad and can refer to any state of health, whether it is optimal or impaired, but it does not specifically denote the inability to function properly as diseases do. An ailment generally refers to a minor illness or a physical disorder that does not carry the same implications of systemic failure as a disease. Thus, "disease" is the most fitting term to describe a condition where the normal function is impaired.