Sakés are usually described with a few words that tell you a lot about what's in the bottle. They're really not that difficult, so we'll try to explain them here.
The first level classification of sake refers to how much of the rice grain has been milled away. In the world of sushi rice, after the husk has been removed typically only 10% of the rice is "polished" away.
But before the brewing process begins, the saké maker wants to remove the oils and proteins that interfere with the subtle flavors the brewer seeks. The goal of milling these starchy rice varieties is to get down to the soft center of the rice, without cracking the grain. Thus the use of rice species with hard exteriors to withstand milling, along with absorbent cores that will get better results from the steaming.
Some brewers have been known to go down to only one third of the rice core remaining. But one has to wonder if there's really a benefit. The yield is small and so the price for this will be expensive. The difference is marginal, and yet the philosophy is that the soul of the rice lies in the last one percent so if it's somehow possible to mill it to this level it's worth doing.
Often you'll see the term junmai used together with ginjō and daiginjō. That's because junmai has another meaning aside form the rice milling. Junmai refers to "pure" saké; e.g. made from only rice and water; no added alcohol. The Japanese government used to require that the term junmai be used only when the rice was milled down to 70% of its original weight. But a "pure" saké made from rice polished down to 50% with no added brewer's alcohol added, can properly be called junmai daiginjō.
Sometimes the brewer adds distilled alcohol to a batch of saké. in order to fortify the cheapest varieties of sake, that's true. But some of the best saké varieties also use this technique with great success to bring out subtle flavorings. You see saké can be brewed to 20% alcohol levels or more before the yeast dies. But it's common to dilute the saké with water, down to around a 15% alcohol level before bottling. Undiluted saké (at original strength) is called genshu.
The three "un"s:
After brewing there is a lot of sediment. Filtering can be done by pressing through mesh or carbon filtering. Saké was traditionally hung in cloth bags to filter, or mechanically pressed through mesh to remove the larger particles, and the result was muroka, which means "unfiltered". Many types of saké today are filtered through loose mesh and still remain cloudy. They are called "nigori". Finally there is carbon filtering, which removes most of the impurities that can mask the saké's intended flavor, but it can at times remove a fair amount of that flavor as well. Most clear saké today is carbon filtered.