—n. 1. a central point, as of attraction, attention, or activity: The need to prevent a nuclear war became the focus of all diplomatic efforts. 2. Physics.a point at which rays of light, heat, or other radiation, meet after being refracted or reflected.
3. Optics. a. the focal point of a lens.
b. the focal length of a lens.
c. the clear and sharply defined condition of an image.
d. the position of a viewed object or the adjustment of an optical device necessary to produce a clear image: in focus; out of focus. 4. Geom.(of a conic section) a point having the property that the distances from any point on a curve to it and to a fixed line have a constant ratio for all points on the curve. See diag. under ellipse, hyperbola, parabola. 5. Geol.the point of origin of an earthquake.
6. Pathol.the primary center from which a disease develops or in which it localizes.
—v.t. 1. to bring to a focus or into focus: to focus the lens of a camera. 2. to concentrate: to focus one's thoughts.