The focus point The focus point on the axis of a lens or mirror to which parallel rays of light converge or from which they appear to diverge after refraction or reflection.
This is an example of a focus point.
How does focus work on a camera? To allow your image to be sharp the camera and lens work together to change the distance of the lens from the sensor in order to control where the captured light converges. When the light converges precisely at the plane of the film or sensor, the image is in focus.