In a scientific experiment, a variable is any factor, trait, or condition that can exist in differing amounts or types. These are the things that can be changed or measured in an experiment.

Here's a breakdown:

* Independent variable: The factor that is manipulated or changed by the experimenter. It's the "cause" in a cause-and-effect relationship. Think of it as the "treatment" applied in the experiment.

* Dependent variable: The factor that is measured or observed in response to the independent variable. It's the "effect" in a cause-and-effect relationship. Think of it as the outcome of the experiment.

* Controlled variable: Factors that are kept constant throughout the experiment to ensure that only the independent variable affects the dependent variable. These are the things you want to remain the same to isolate the effects of the independent variable.

Example:

Let's say you're testing the effect of different fertilizers on plant growth.

* Independent variable: Type of fertilizer (e.g., fertilizer A, fertilizer B, no fertilizer)

* Dependent variable: Plant height (measured in centimeters)

* Controlled variables: Amount of water, sunlight, type of soil, plant species.

Understanding variables is crucial for designing and interpreting experiments because it helps us isolate and understand the relationship between cause and effect.