Single-malt whiskies (often just called 'malts') are whiskies made purely of malted barley. What makes them special and so distinctive is where they come from and how they are distilled. So, for example, a malt from the island of Islay will be quite briney, almost salty, while a Speyside malt will be slightly sweeter and more delicate. A malt from the likes of Deeside will be slightly more smoky and a little more peaty. The ageing process helps to accentuate each single-malt whisky's individual characteristics. A blended whisky, conversely, is a mix of some mature malts, along with some very young grain whisky.
As with wine, it takes time to get to know the complexities and personalities of different types of whisky, particularly single-malts.