Focus
FOCUS (Latin for "hearth" or "fireplace"), a point at which converging rays meet, toward which they are directed, or from which diverging rays are directed; in the latter case called the virtual focus (see Microscope; Telescope; Lens). In geometry the word is used to denote certain points (see Geometry; Conic Section; and Perspective).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
