a subject that is being discussed or studied : the subject on which people's attention is focused—usually singular
a main purpose or interest
a point at which rays of light, heat, or sound meet or from which they move apart or appear to move apart; especially : the point at which an image is formed by a mirror, a lens, etc.
2focusverb
to cause (something, such as attention) to be directed at something specific—+ on
to direct your attention or effort at something specific —often + on
to adjust (something, such as a lens or a camera) to make an image clear
