There are several definitions that you need to know about experimental design.

Extraneous variable:undesirable variables that influence the relationship between the variables that an experimenter is examining

Control group:A control group uses a control group to compare to an experimental group in a test of a hypothesis. The control and experimental groups must be identical in all ways except for the introduction of a suspected causal agent into the experimental group.

Variables: Any changed factor used to test a hypothesis or prediction that could effect the results.

Independent variable: A variable that you purposely change.

Dependent Variable: A variable that you can't change.

Control Variable: The conditions that are kept the same in a scientific investigation.

Control: A standard condition against which other conditions can be compared in an experiment.