Dictionary

(followed by on or upon) To concentrate one's attention.

Example: I have to focus on my work.

To cause (rays of light, etc) to converge at a single point.

To adjust (a lens, an optical instrument) in order to position an image with respect to the focal plane.

Example: You'll need to focus the microscope carefully in order to capture the full detail of this surface.

To concentrate one’s attention.

Example: If you're going to beat your competitors, you need to focus.

Directing all one's efforts towards achieving a particular goal.

Dealing with some narrowly defined aspects of a broader phenomenon.