Definition for foci (2 of 2)
noun, plural fo·cus·es, fo·ci [foh-sahy, -kahy] /ˈfoʊ saɪ, -kaɪ/.
- the focal point of a lens, on which rays converge or from which they deviate.
- the focal length of a lens; the distance from a focal point to a corresponding principal plane.
- 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.
verb (used with object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.
verb (used without object), fo·cused, fo·cus·ing or (especially British) fo·cussed, fo·cus·sing.
Origin of focus
Examples from the Web for foci
The circle has one focus at the centre, an ellipse or hyperbola two foci equidistant from the centre.
In the old times of Roman domination the encampments of the legions in the provinces had always proved to be foci of civilization.History of the Conflict Between Religion and Science|John William Draper
But the orbits are elliptical, and the Sun holds a position in one of the foci of each ellipse.Astrology|Sepharial
Their physicians were their great philosophers; their medical colleges were their foci of learning.History of the Intellectual Development of Europe, Volume I (of 2)|John William Draper
The curve thus traced will be an ellipse having the pins at the two points which are called its foci.A Text-Book of Astronomy|George C. Comstock