focus

n. pl. fo·cus·es or fo·ci (-s, -k)
1.
a. A point at which rays of light or other radiation converge or from which they appear to diverge, as after refraction or reflection in an optical system: the focus of a lens. Also called focal point.
b. See focal length.
2.
a. The distinctness or clarity of an image rendered by an optical system.
b. The state of maximum distinctness or clarity of such an image: in focus; out of focus.
c. An apparatus used to adjust the focal length of an optical system in order to make an image distinct or clear: a camera with automatic focus.
3. A center of interest or activity. See Synonyms at center.
4. Close or narrow attention; concentration: "He was forever taken aback by [New York's] pervasive atmosphere of purposefulnessthe tight focus of its drivers, the brisk intensity of its pedestrians" (Anne Tyler).
5. A condition in which something can be clearly apprehended or perceived: couldn't get the problem into focus.
6. Pathology The region of a localized bodily infection or disease.
7. Geology The point of origin of an earthquake.
8. Mathematics A fixed point whose relationship with a directrix determines a conic section.