Randomized Controlled Trials are experimental studies where an intervention is applied to one group and the other group (control) does not get the intervention or gets placebo. Typically, subjects are randomized into the intervention or control group..
Koffel, 2011.
NOTE: There are also experimental designs with no randomization. These are called Quasi-Experimental Studies. See Joanna Briggs Institute's Checklist for Quasi-Experimental Studies to appraise the validity of the study,