focus

1. focus (noun) — sense 1

Definition: A point at which reflected or refracted rays of light converge.

Example: The heat of sunlight at the focus of a magnifying glass can easily set dry leaves on fire.

2. focus (noun) — sense 2

Definition: A point of a conic at which rays reflected from a curve or surface converge.

3. focus (noun) — sense 3

Definition: The fact of the convergence of light on the photographic medium.

Example: Unfortunately, the license plate is out of focus in this image.

4. focus (verb) — sense 4

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

Example: 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.

5. focus (verb) — sense 5

Definition: 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.

6. focus (verb) — sense 6

Definition: To adjust itself or be adjusted such that light from a scene converges appropriately to create a clear image.

Example: I can't get the lens to focus.