Definition of focus

• n. - A point in which the rays of light meet, after being reflected or refrcted, and at which the image is formed; as, the focus of a lens or mirror.
• n. - A point so related to a conic section and certain straight line called the directrix that the ratio of the distace between any point of the curve and the focus to the distance of the same point from the directrix is constant.
• n. - A central point; a point of concentration.
• v. t. - To bring to a focus; to focalize; as, to focus a camera.