Main Entry: ¹fo·cus

Pronunciation: \ˈfō-kəs\

Function: noun

Inflected Form(s): plural fo·ci \ˈfō-ˌsī also -ˌkī\ also fo·cus·es

1 a : a point at which rays (as of light, heat, or sound) converge or from which they diverge or appear to diverge ; specifically : 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 system b : a point of convergence of a beam of particles (as electrons)
2 a : focal length b : adjustment for distinct vision ; also : the area that may be seen distinctly or resolved into a clear image
3 : a localized area of disease or the chief site of a generalized disease or infection