Positive control

The term positive control has several meanings.

Usage in experimental design
A positive control is an experimental procedure that causes a known effect when applied to a sample population.

The positive control in experiments reveals that a certain procedure works according to expectations and actually gives you the expected results. It shows that the experiment is functioning as it should; in practice this means that your subject(s) are exposed to a substance or procedure with a known effect.

Contrast this with the negative control, (or standard scientific control) where you expose your subject to a substance or condition that is known to have no effect.

Phrase
One says that positive control has been achieved when what happens is what was intended to happen and that's all that happens.