focus
n. C / Un. the main point of interest or attention. It can also mean the clear image you see through a camera or glasses.
n. the centre of interest or activity; the state or quality of having a clear visual image. Often used to describe the concentration of attention on a specific subject.
The main focus of the meeting is the new budget.
The photographer adjusted the lens until the subject's eyes were in sharp focus against the blurred background.
While the initial report touched on several minor issues, the primary focus remains the structural integrity of the bridge and the immediate safety of commuters.
Borrowed from Latin focus (“hearth, fireplace”); see there for more. Related to fuel. Kepler introduced the term into mathematics and the sciences in describing elliptical orbits of planets (quote from Nicholas Mee) : "One of the interesting properties of an ellipse is that if there were a light bulb at one focus, then all the light that it emits would reflect off the ellipse and converge at the other focus. This is why Kepler originally used the name focus for these points."
Often used with the preposition 'of' to indicate the subject of attention, or in the phrase 'in focus' to describe visual clarity.
the focus on the problem is importantthe focus of the problem is importantWhile you 'focus on' something (verb), the noun form often takes 'of' when identifying the central point, though 'focus on' is increasingly common in modern usage.