A dependent variable is the variable in a scientific experiment that's being tested. An independent variable is the variable that can be changed during the course of an experiment to study the affect on the dependent variable.
The dependent variable is the primary object of study in any experiment, and it does not change throughout the course of the experiment. Different independent variables may be used throughout the course of an experiment to determine what impact, if any, the change has on the dependent variable. When results of an experiment are put on a graph, the independent variable is on the X-axis and the dependent variable is on the Y-axis.