Another gray area between recreational and technical diving involves the differences in diving depths and times and their relation to decompression practices.
As some may know, I published an article a couple years ago on current thinking about ascent strategies in decompression diving. I tried to do the same thing for NDL diving, but I could not find enough definitive research to support any conclusions. I asked some experts for help, but they refused, saying that there is not enough definitive research to support any conclusions. The research I did before quitting the project clearly told me there is very much a difference between what we commonly call NDL, sport, or recreational dives and what we call decompression dives. With NDL dive, once you begin an ascent from depth, your ascent rate does not seem to matter, provided you are not going too fast to off-gas or so slow you violate NDLs. With decompression diving, the rate at which you ascend, including deco stops, very much matters.
The problem is that there is no bright line between the two. That is why we have a gray area. You can see the beginning of the gray area in the old PADI tables. The optional safety stops are recommended for most dives, but once you get to the deeper dives and/or closer to the NDLs, those optional safety stops become mandatory, creating an oxymoron that has befuddled divers for decades. You can also see it in the discussion a few posts above this about the decompression stops that are a part of BSAC training.
Summary: We call dives that absolutely allow the diver to go right to the surface sport, or recreational, or NDL dives (or whatever you prefer). We call dives that demand decompression stops before surfacing technical diving. In between, there is a gray area where we have mandatory optional safety stops or what some people call "lite deco." People who are comfortable with gray areas aren't bothered by this. Others want the gray areas eliminated so that all diving fits into one category or another.