The distance of the near clipping plane from the the Camera, in world units.
The near clipping plane is nearest point of the Camera's view frustum. The Camera cannot see geometry that is closer this distance. For more information, see Understanding the view frustum.
In the Unity Editor, this corresponds to the Clipping Planes: Near property in the Camera component Inspector.
Additional resources: Camera Inspector reference, Camera.farClipPlane, layerCullDistances.