What is a dependent variable mean in science fair?

Typically in an experiment there will be one or more conditions that are varied while one or more other conditions are monitored and measured. The first type of condition is considered the independent variable, while the second type, the type you measure while varying the first, is called the dependent variable. For example, you might vary the weight of the mass at the bottom a pendulum while measuring the period of the pendulum when it is swung. The weight of the mass is the independent variable while the period is the dependent variable in this case.