**Core Concept**
Sensitivity in the context of medical testing refers to the ability of a test to correctly identify individuals with a particular disease or condition. It is a measure of the test's ability to detect true positives, where a positive result is correctly attributed to the presence of the disease.

**Why the Correct Answer is Right**
Sensitivity is calculated as the number of true positives (correctly identified cases) divided by the sum of true positives and false negatives (missed cases). In other words, it measures the proportion of people with the disease who test positive. A highly sensitive test will have fewer false negatives, meaning it will be better at detecting individuals with the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Specificity is a related concept that measures the test's ability to correctly identify individuals without the disease, and is not the definition of sensitivity.
**Option B:** Predictive value is a measure of the probability that a positive result indicates the presence of the disease, and is not a direct measure of the test's ability to detect true positives.
**Option C:** Accuracy is a broader measure that combines sensitivity and specificity, and is not a direct measure of the test's ability to detect true positives.

**Clinical Pearl / High-Yield Fact**
Remember that sensitivity and specificity are both important measures of a test's performance, but they are not interchangeable terms. A highly sensitive test may have a lower specificity, and vice versa.

**Correct Answer:** . True Positive Rate.