In the section Understanding the View Frustum, it was explained that any point in the cameraA component which creates an image of a particular viewpoint in your scene. The output is either drawn to the screen or captured as a texture. More info
See in Glossary’s view corresponds to a line in world space. It is sometimes useful to have a mathematical representation of that line and Unity can provide this in the form of a Ray object. The Ray always corresponds to a point in the view, so the Camera class provides the ScreenPointToRay and ViewportPointToRay functions. The difference between the two is that ScreenPointToRay expects the point to be provided as a pixelThe smallest unit in a computer image. Pixel size depends on your screen resolution. Pixel lighting is calculated at every screen pixel. More info
See in Glossary coordinate, while ViewportPointToRay takes normalized coordinates in the range 0..1 (where 0 represents the bottom or left and 1 represents the top or right of the view). Each of these functions returns a Ray which consists of a point of origin and a vector which shows the direction of the line from that origin. The Ray originates from the near clipping planeA plane that limits how far or close a camera can see from its current position. A camera’s viewable range is between the far and near clipping planes. See far clipping plane and near clipping plane. More info
See in Glossary rather than the Camera’s transform.position point.