A Z-Test is a statistical method used to determine if there is a significant difference between the means of two groups. It is particularly useful when the sample size is large (typically over 30) and the population variance is known. The test compares the sample mean to a known population mean, helping researchers understand if observed differences are due to random chance or if they reflect a true effect. To perform a Z-Test, you calculate the Z-score, which measures how many standard deviations a sample mean is from the population mean. If the Z-score exceeds a certain threshold, it indicates that the difference is statistically significant, allowing researchers to make informed conclusions about their data.