**Core Concept**
Frequency distribution is a statistical method used to represent the number of observations within a given range or interval. It is a way to visualize the distribution of data, helping to identify patterns and trends. In epidemiology and public health, frequency distributions are essential for understanding the characteristics of populations and making informed decisions.

**Why the Correct Answer is Right**
A histogram is a graphical representation of frequency distribution, where the x-axis represents the values or categories of the data, and the y-axis represents the frequency or number of observations within each category. Histograms are particularly useful for displaying the distribution of continuous data, such as age, height, or weight. The bars in a histogram are typically adjacent to each other, allowing for easy comparison of the frequency of different values.

**Why Each Wrong Option is Incorrect**
**Option B:** Line diagrams are used to show trends or relationships between two or more variables over time, but they are not suitable for displaying frequency distributions.
**Option C:** Pie diagrams are used to show the proportion of different categories within a dataset, but they are not suitable for displaying frequency distributions.
**Option D:** There is no such thing as a "Ski diagram" in statistics or epidemiology, making it an incorrect option.

**Clinical Pearl / High-Yield Fact**
When analyzing frequency distributions, it is essential to consider the shape of the distribution, including whether it is skewed or normal. This can provide valuable insights into the underlying characteristics of the population and inform public health interventions.

**✓ Correct Answer: A. Histogram. A graphical representation of frequency distribution, used to display the number of observations within a given range or interval.**