Single malt Scotch whisky, by definition, is produced entirely from malted barley and no other grains, in pot stills (as opposed to column stills), and at a single distillery. In the United States, whisky's labeled as “American Single Malt” have to follow those same rules, and also be distilled up to a strength of 160 proof and aged in oak of up to 700 liters. Single malts are also produced in Japan, Australia, and beyond.
Blended Malt Scotch Whisky, on the other hand, can be made of a blend of single malts from multiple distilleries; and Blended Scotch Whisky is a blend of Single Malt Scotch Whisky and Single Grain Scotch Whisky.