**Core Concept**
The confidence interval (CI) is a statistical measure used to express the reliability or precision of a sample estimate. It represents the range of values within which the true population parameter is likely to lie. The upper and lower boundaries of the CI are crucial in determining the precision of the estimate.

**Why the Correct Answer is Right**
The upper and lower boundaries of the confidence interval are termed as the **upper limit** and **lower limit**, respectively. These limits are calculated using the standard error (SE) of the estimate and the critical value from the standard normal distribution (Z-score) corresponding to the desired confidence level. The formula for calculating the CI is: CI = estimate ± (Z-score × SE). The upper limit is the estimate plus the product of the Z-score and SE, while the lower limit is the estimate minus the product of the Z-score and SE.

**Why Each Wrong Option is Incorrect**
**Option A:** is incorrect because it is a term used to describe the middle value of the CI, not the upper or lower boundaries.
**Option B:** is incorrect because it is a statistical term used to describe the dispersion of data, not the limits of the CI.
**Option C:** is incorrect because it is a term used to describe the precision of the estimate, not the upper or lower boundaries of the CI.

**Clinical Pearl / High-Yield Fact**
When interpreting a CI, it is essential to consider the sample size, study design, and desired confidence level to determine the width of the CI and its reliability. A narrower CI indicates greater precision, while a wider CI suggests less precision.

**Correct Answer: C. Upper and lower limits**