## **Core Concept**
The question tests the understanding of epidemiological terms, specifically the definition of incidence. **Incidence** refers to the number of new cases that develop in a specified time period among a population at risk.

## **Why the Correct Answer is Right**
The correct answer, **Incidence**, is the measure of new cases occurring in a defined population during a specified period of time. This concept is crucial in epidemiology to understand the rate of occurrence of a disease. It helps in assessing the risk of developing a particular condition.

## **Why Each Wrong Option is Incorrect**
- **Option A: Prevalence** - This is incorrect because prevalence refers to the total number of cases (new and existing) of a disease in a population at a given time, not just new cases.
- **Option B: Point Prevalence** - This is incorrect because point prevalence is a snapshot of the prevalence at a specific point in time, not the rate of new cases over a period.
- **Option C: Period Prevalence** - This is incorrect because period prevalence includes all cases (new and existing) over a specified period, not just the new cases.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **incidence rate** is often expressed as the number of new cases per 1,000 or 100,000 population per year, which helps in comparing the risk across different populations or over time.

## **Correct Answer:** C. Incidence.