A dependent variable is basically the outcome or result that you're trying to measure or explain, it's the thing that changes in response to something else. For example, if you're studying how different amounts of fertilizer affect the growth of plants, the growth of the plants would be the dependent variable because it's the outcome you're measuring, whereas the amount of fertilizer would be the independent variable because it's the thing you're changing on purpose. Another example could be how the temperature outside affects the number of people who buy ice cream, in this case, the number of people buying ice cream is the dependent variable and the temperature is the independent variable.
