Latin focus (“hearth, fireplace”), of unknown origin. Usually connected with Old Armenian բոց (bocʿ).
focus (countable and uncountable; plural foci or focuses)
- (countable, optics) a point at which reflected or refracted rays of light converge.
- The heat of sunlight at the focus of a magnifying glass can easily set dry leaves on fire.
- (countable, geometry) a point of a conic at which rays reflected from a curve or surface converge.
- (uncountable, photography, cinematography) The fact of the convergence of light on the photographic medium.
- Unfortunately, the license plate is out of focus in this image.
- (uncountable, photography, cinematography) The quality of the convergence of light on the photographic medium.
- During this scene, the boy’s face shifts subtly from soft focus into sharp focus.
- (uncountable) concentration of attention.
- I believe I can bring the high degree of focus required for this important job.
- (countable, seismology) the exact point of where an earthquake occurs, in three dimensions.
- The earthquake's focus was at exactly 37 degrees north, 18 degrees south, seventy five meters below the ground.
- (computing, graphical user interface) The indicator of the currently active element in a user interface.
- Text entered at the keyboard or pasted from a clipboard is sent to the component which currently has the focus.
- (linguistics) The most important word or phrase in a sentence or passage, or the one that imparts information
fact of the convergence of light on the photographic medium
quality of the convergence of light on the photographic medium
concentration of attention
exact point of where an earthquake occurs
focus (third-person singular simple present focuses or, less commonly, focusses, present participle focusing or, less commonly, focussing, simple past and past participle focused or, less commonly, focussed)
- (transitive) To cause (rays of light, etc) to converge at a single point.
- (transitive) To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.
- You'll need to focus the microscope carefully in order to capture the full detail of this surface.
- (transitive, followed by on or upon) To concentrate one's attention.
- Focus on passing the test.
- (transitive) To make (a liquid) less diluted.
- (intransitive) To concentrate one’s attention.
- If you're going to beat your competitors, you need to focus.
Usage notes 
The spellings focusses, focussing, focussed are observed in Commonwealth English while the spellings focuses, focusing, focused are preferred in the US.
Derived terms 
Related terms 
cause (rays of light, etc) to converge at a single point
to adjust (a lens, an optical instrument)
transitive: to concentrate one's attention
make (a liquid) less diluted
intransitive: to concentrate one's attention
Borrowed from Latin focus, whence also Italian fuoco (an inherited doublet).
focus m (invariable)
- focus (all senses)
The origin is uncertain. Usually connected with Old Armenian բոց (bocʿ).
focus (genitive focī); m, second declension
- hearth, fireplace
Derived terms 
Related terms