An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear, Close or narrow attention; concentration, uncountable concentration of attention, transitive verb_ To bring to a focus; to focalize; as, to focus a camera, intransitive verb_ To direct toward a particular point or purpose, To adjust (a lens, for example) to produce a clear image

Of or relating to a focus, Placed at or measured from a focus, Belonging to, concerning, or located at a focus