Experiments are the backbone of scientific endeavors. But they should be carried out with utmost care and control so that you are sure nothing external and unwanted influences the outcome. There are certain terms associated with experiments that form the basis of experimental knowledge.

While conducting an experiment, the variable that you control, vary or alter is called the Independent variable. It is independent in that it does not depend on anything, rather free to be altered and is being manipulated by you.

The dependent variable is the one that responds to the changes in the independent variable. It's the outcome variable, the one that you are observing.

The constant is the term or factor that remains the same despite the changes in the independent variable. They are most often defined values that cannot be altered like Avogadro's number or pi. You will either have prior knowledge about their role in the experiment or they will come out while making calculations.

The control group is a benchmark or reference that you use to compare your current experimental results with. It is the group or setup you are not conducting the experiment on, is isolated from any influences, left alone, but identical to the experimental setup before the experiment started.

In an easy example of an experiment on Ohm's law, the current values are observed by varying the voltage across a conductor. The voltage is the independent variable that is being varied, the current is the dependent variable as it responds and the constant comes out to be the resistance of the conductor.