More or less everything seems to have been already said on this, but still I'd like to add my perspective on this.
It's clear that the original question is not about the definition of enema, and the word "real" does not refer to any definition that is reported on any dictionary. Otherwise, the person who started this thred would have simply looked into the dictionary and would have not bothered coming here and ask.
So, the way I see the question is: whatever the definition of an enema is, which is the amount of solution that makes an enema a satisfying experience?
If this is the question (of course I might misinterpret), I would say that yes, even a few drops of liquid injected in the rectum is technically an enema, but that is here pretty much irrelevant. More relevant would be to know whether the perspective to use for evaluating the enema is the sexual pleasure, the relief from constipation, the overall well-being, or any other.
On this my view is that really a small amount can be as good as a large one, depending on personal tastes. I happened to play with some fleet enemas, and even though that is certainly not my favorite equipment, with the right company the experience was great enough, with a quite small volume. Other parameters make the experience more or less satisfying, also depending on the final goal of the enema.
But as usual, different people might have different perceptions, and I can easily understand that for some an enema with a volume under one or even two quarts does not even qualify as an enema. This is certainly the case if you are used to take large enemas... in this case a small one is not even perceived as an enema!
As I have never taken more than 1.5 quarts, I would say that the level of satisfaction for me does not come from the volume. Also half a quart can be fantastic. But that's the beauty of it, we are all different, and each of us has his/her own truth, especially when it comes to our feelings.
Enjoy!