A confidence interval is a statistical tool used to estimate the range within which a population parameter, such as the mean, is likely to fall. It is derived from sample data and provides a lower and upper limit, indicating the degree of uncertainty associated with the estimate. For instance, a 95% confidence interval suggests that if we were to take multiple samples, approximately 95% of those intervals would contain the true population mean. This concept is crucial in data analysis and machine learning, as it helps quantify the reliability of estimates and informs decision-making processes.