A confounding variable is an external factor that can influence both the independent and dependent variables in a study, potentially leading to misleading results. For example, if researchers are studying the effect of exercise on weight loss, a confounding variable could be diet, as it also affects weight loss and may vary among participants. Identifying and controlling for confounding variables is crucial in research to ensure that the observed effects are truly due to the independent variable. Failure to account for these variables can result in incorrect conclusions, making it difficult to establish a clear cause-and-effect relationship.