- 1. (F) The point at which the light rays meet after passing through a convex lens. 2. The center, or the starting point, of a disease process. [L. a hearth]- conjugate foci two points so related to a lens or concave mirror that an image at one point is focused at the other, and vice versa.- natural f. of infection an ecosystem in which an infectious agent normally persists in nature; e.g., yellow fever virus in a jungle monkey-Haemagogus mosquito ecosystem.- virtual f. the point from which divergent rays seem to proceed, or that at which they would meet if prolonged backward.
* * *1 a) a point at which rays (as of light, heat, or sound) converge or from which they diverge or appear to diverge specif the point where the geometrical lines or their prolongations conforming to the rays diverging from or converging toward another point intersect and give rise to an image after reflection by a mirror or refraction by a lens or optical systemb) a point of convergence of a beam of particles (as electrons)2 a) FOCAL LENGTHb) adjustment for distinct vision also the area that may be seen distinctly or resolved into a clear image3) a localized area of disease or the chief site of a generalized disease or infection1) to bring (as light rays) to a focus2 a) to adjust the focus of (as the eye or a lens)b) to bring (as an image) into focus vi1) to come to a focus2) to adjust one's eye or a camera to a particular rangefo·cus·able -kəs-ə-bəl adj
* * *1. n. the point at which rays of light converge after passing through a lens.2. n. the principal site of an infection or other disease.
* * *fo·cus (foґkəs) pl. foґci [L. â€œfire-placeâ€] 1. the point of convergence of light rays or of the waves of sound. 2. the chief center of a morbid process. 3. cardiac pacemaker.
Medical dictionary. 2011.