Independent variables are the variables that are manipulated or altered in an experiment to determine their effect on a dependent variable. They are sometimes referred to as "predictor variables" or "explanatory variables." In an experiment, the independent variable is typically what the researcher changes to observe how it affects the outcome, which is measured by the dependent variable.
For example, if a scientist is studying the effect of different amounts of sunlight on plant growth, the independent variable would be the amount of sunlight each plant receives, while the dependent variable would be the growth of the plants, usually measured in height or biomass.