Definition of "focus"

focus

/ˈfəʊ.kəs/

noun
countable and uncountable, plural foci or focuses or focusses
1. (countable, optics) A point at which reflected or refracted rays of light converge.
2. (countable, geometry) A point of a conic at which rays reflected from a curve or surface converge.
3. (uncountable, photography, cinematography) The fact of the convergence of light on the photographic medium.
  Quotations
  Not long ago, it was difficult to produce photographs of tiny creatures with every part in focus. […] A photo processing technique called focus stacking has changed that. Developed as a tool to electronically combine the sharpest bits of multiple digital images, focus stacking is a boon to biologists seeking full focus on a micron scale.
  2013 July-August, Catherine Clabby, “Focus on Everything”, in American Scientist
4. (uncountable, photography, cinematography) The quality of the convergence of light on the photographic medium.
5. (uncountable) Concentration of attention.
6. (countable, seismology) The exact point of where an earthquake occurs, in three dimensions (underneath the epicentre).
7. (graphical user interface) The status of being the currently active element in a user interface, often indicated by a visual highlight.
8. (linguistics) The most important word or phrase in a sentence or passage, or the one that imparts information.
9. An object used in casting a magic spell.
  Quotations
  Candles, in fact, are an essential ingredient in many spells. They can be used as either the focus of the spell or as a component that sets the spell's overall mood and tone.
  2004, Marian Singer, Trish MacGregor, The Only Wiccan Spell Book You'll Ever Need
  I ran through what I knew about spells from Mom and other witchcraft sources, but nothing matched what I was used to seeing in her magic work. Usually she used herbs and other plants as a focus for the spell.
  2014, Kristen S. Walker, Witch Gate, page 180
verb
third-person singular simple present focuses or focusses, present participle focusing or focussing, simple past and past participle focused or focussed
1. (transitive) To cause (rays of light, etc) to converge at a single point.
  Quotations
  The difficulties of focussing colour-light signals on curved tracks to ensure maximum sighting distance were underlined in the recent official report [...] on a low-speed collision at Newcastle Central on July 25, 1960, between an unfitted freight and a diesel-hauled passenger train.
  1961 February, “Talking of Trains: Collision at Newcastle”, in Trains Illustrated, pages 75–76
2. (transitive, optics) To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.
3. (intransitive, optics, of a lens, optical instrument, etc.) To adjust itself or be adjusted such that light from a scene converges appropriately to create a clear image.
4. (transitive) To direct attention, effort, or energy to a particular audience or task.
5. (intransitive) To concentrate one’s attention.
6. (intransitive, followed by on or upon) To concentrate one's attention on something; to have as one's central point of interest, concern, etc.
7. (computing, graphical user interface, transitive) To transfer the input focus to (a visual element), so that it receives subsequent input.
8. (accounting, formerly) To aggregate figures of accounts.
  Quotations
  Whole pages of it are filled with masses of figures, generally single numbers added up in batches, and then the totals added in batches again, as though he were "focusing" some account, as the auditors put it.
  1897, Bram Stoker, Dracula, published 1993, page 67