**Core Concept**
A bimodal distribution is a type of probability distribution in statistics where two distinct peaks are observed, indicating the presence of two separate populations or subpopulations within a dataset. This phenomenon is often seen in medical research when analyzing continuous variables, such as blood pressure or body mass index.

**Why the Correct Answer is Right**
In a bimodal distribution, two distinct modes are present, which can be attributed to the presence of two separate populations or subpopulations. For instance, in a study examining the distribution of blood pressure in a population, a bimodal distribution might indicate the presence of two distinct subpopulations, one with normal blood pressure and another with hypertension. The exact mechanisms underlying bimodal distributions can be complex and may involve various factors, including genetic, environmental, or lifestyle factors.

**Why Each Wrong Option is Incorrect**
**Option A:**
A normal distribution, also known as a Gaussian distribution, is characterized by a single peak and a continuous range of values, which is the opposite of a bimodal distribution.

**Option B:**
A skewed distribution is a type of distribution where the data is not symmetric around the mean, but it can still have a single peak, unlike a bimodal distribution.

**Option C:**
A multimodal distribution is a type of distribution that has more than two peaks, which is a more general term that encompasses bimodal distributions but is not the same thing.

**Clinical Pearl / High-Yield Fact**
When analyzing continuous variables, a bimodal distribution can indicate the presence of two distinct subpopulations, which can have significant implications for research and clinical practice.

**Correct Answer: D.**