ArchVis for interiors

I do use a PPV and LMIV. I am able to accomplish a close-to realistic appearance, but in all honesty, I think it could be much better from what I have seen on the web. Can you explain IES lights? I am sure I have heard of them but from the acronym I cant figure out what is stands for. Also, could you explain what/where and HDRI cube map is and what GI stands for?