RF energy (short for radio frequency energy) was a form of energy used to power sections of starships and space stations.
The infirmary on Deep Space 9 utilized RF energy, and in 2370, exposure to Gamma Quadrant gas morphed Constable Odo into a destructive creature that absorbed low frequency RF energy. Chief O'Brien used bursts of RF energy to lead Odo into a force field trap in order to contain him. (DS9: "The Alternate")