ED = glass coating, just a marketing ploy really.

N = a better glass coating

IF = Internally focused. Focus is handled by the internal elements of the lens, and not the front element.

DX = Useful bit of information telling you the lens will only work on APS-C cameras and if used on Full Frame cameras will limit your resolution quite a lot.

via What is a Nikon ED DX Lens? – The Photo Forum – Photography Discussion Forum.

What is APS-C?