Malt Whisky is produced only from 100% malted barley.
To be a single malt, the whisky must have been distilled at a single distillery using the pot still distillation process and made from a mash of 100% malted barley. And the "Scotch" part? That means it's from Scotland! You can have single malt Irish Whiskey, Japanese, etc. And while there are undoubtedly many worthy whiskies to be tried from these other shores, any journey of discovery into the world of single malts should most certainly start, and indeed finish, in Scotland.