fo•cus(fō′kəs),USA pronunciationn., pl.-cus•es, -ci(-sī, -kī),USA pronunciationv.,-cused, -cus•ing or (esp. Brit.) -cussed, -cus•sing. n.
a central point, as of attraction, attention, or activity:The need to prevent a nuclear war became the focus of all diplomatic efforts.
Physicsa point at which rays of light, heat, or other radiation, meet after being refracted or reflected.
the focal point of a lens.
the focal length of a lens.
the clear and sharply defined condition of an image.
the position of a viewed object or the adjustment of an optical device necessary to produce a clear image:in focus; out of focus.
Mathematics[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.
Geologythe point of origin of an earthquake.
[Pathol.]the primary center from which a disease develops or in which it localizes.
to bring to a focus or into focus:to focus the lens of a camera.
to concentrate:to focus one's thoughts.
to become focused.
Latin: fireplace, hearth
1.See corresponding entry in Unabridged center, heart, core, nucleus.