For those not familiar with the distinctions of the whisky world, a single malt whisky contains only malt whisky from a single distillery. A blended whisky such as Johnnie Walker or Bell's contains a mixture of malt and grain whiskies from a range of distilleries. "Pure malts" - or as some fundamentalist single malt buffs somewhat hopefully want them to be called, "vatted malts" - sit somewhere in between the two: containing only malt whisky but from more than one distillery.
Two more peripheral categories: a single cask whisky is a single malt that not only comes from only one distillery but one cask. You can also get single grain whiskies, taking the grain whisky usually used in blends and issuing it on its own. These last are rare and I have never tried one. People say they are not inferior.
These are the main categories that concern whisky distilled in the Scottish tradition, of which Japanese whisky is broadly part. There are others for Irish and US whiskey.