From the FAA controller's handbook:
4-8-7. SIDE-STEP MANEUVER
Side-step Maneuver. When authorized by an instrument approach procedure, you may clear an aircraft for an approach to one runway and inform the aircraft that landing will be made on a parallel runway.
EXAMPLE-
"Cleared I-L-S Runway seven left approach. Side-step to runway seven right.”
NOTE-
Side-step maneuvers require higher weather minima/ MDA. These higher minima/MDA are published on the instrument approach charts.