When referring to a DSLR camera lens what is the meaning of 10.5mm f2.8G ED?

10.5 mm refers to the focal length of the lens. f2.8 refers to the lens aperture.

ED indicates the presence of at least one Extra-low Dispersion glass element in the lens with the purpose of minimizing the chromatic aberration for a better colour rendition. If I correctly argued the contest you are referring to (a Nikon DX Format digital SLR camera)... this focal length corresponds to a fish eye lens with a 180° angle of view and

G indicates that this is a G-type Nikkor lens, designed with no aperture rings. Info taken from a Nikon press release.