Junmai: 
Junmai is pure rice saké. Nothing is used in its production except rice, water, yeast, and koji (that magical mold that converts the starch in the rice into fermentable sugars). Junmai is brewed WITHOUT any addition of distilled alcohol. Generally a bit heavier and fuller in flavor than other types of Saké, with slightly higher acidity. Goes well with a wide range of food. Must have seimaibuai of at least 70%, meaning the outer 30% of each rice grain has been polished away.

Tokubetsu Junmai: 
Tokubetsu means "special". Any saké labeled Tokubetsu has been brewed in some special way. In some cases, this may mean a 60% or 50% seimaibuai, or it may mean the saké was fermented at lower temperatures or made with very special saké rice. Tokubetsu Junmai is generally a bit more fragrant and refined than regular Junmai.

Junmai Ginjo:
Indicates a special and painstaking brewing process wherein fermentation proceeds at lower temperatures and for longer periods, and pressing is often done by hand. This extra effort produces a saké that is layered and complex, light and fragrant. Must have a seimaibuai of at least 60%.

Junmai Daiginjo:
Even a more painstaking brewing process than Ginjo, which results in saké that is even lighter and more fragrant and fruity than a typical Ginjo. Must have a seimaibuai of at least 50%. Often, Daiginjo goes as far as a 35% seimaibuai (65% of the kernel polished away!).