Beam steering (also spelled beamsteering or beam-steering) is about changing the direction of the main lobe of a radiation pattern.
In radio systems, beam steering may be accomplished by switching antenna elements or by changing the relative phases of the RF signals driving the elements.
In optical systems, beam steering may be accomplished by changing the refractive index of the medium through which the beam is transmitted or by the use of mirrors, prisms, lenses, or rotating diffraction gratings. Examples of optical beam steering approaches include mechanical mirror-based gimbals or beam-director units, galvanometer mechanisms that rotate mirrors, Risley prisms, phased-array optics, and microelectromechanical systems (MEMS) using micro-mirrors.
Source: from Federal Standard 1037C