Explanatory and Response Variables

When examining the relationship between two variables it can sometimes be seen that one of the variables explains, influences, or determines the other. This kind of variable is called an explanatory variable. Its counterpart (the one that it explains/influences/determines) is called the response variable.

Example:
If you did an experiment to see how tall plants grew given different amounts of water, the explanatory variable would be 'amount of water given', while the response variable would be 'height'.