In
experimentation, 'control' can be used as a noun meaning either the
group which is not
manipulated by the
experimenter, or a measure taken to prevent
confounds (or
counfounding variables) from influencing the results. Example: "The
experimental group took the drug we're testing, while the
control group was treated exactly the same way, except that the pill they were given contained no active ingredient."
Also a verb meaning to take such measures. Example: "We thought that age of the subjects might introduce a confound, so we
controlled for that by selecting only subjects born in May of 1944."