Difference between singal whisky and scotch whisky?

Scotch whiskey is any whiskey (regardless of grain type etc.) that is made in Scotland and produced according to the Scotch Whisky Regulations.

Single whiskey is whiskey that is produced anywhere in the world (unless it's Single Scotch Whisky, Single Irish Whisky etc.) and that comes from exactly one distillery. The distillery may bottle a single barrel or may mix together many different casks - as long as these all come from that one distillery, it's still "single".