An independent variable is a factor in an experiment that is changed or controlled to test its effects on other variables. It is the variable that researchers manipulate to observe how it influences the outcome. For example, in a study examining how different amounts of sunlight affect the growth of plants, the amount of sunlight is the independent variable. In contrast, the dependent variable is what is measured in the experiment. Continuing with the previous example, the growth of the plants would be the dependent variable, as it depends on the amount of sunlight provided. Understanding independent variables is crucial for designing effective experiments.