Whisky is any spirit distilled from fermented grain, to qualify as scotch the spirit must be made from malted barley. Many scotches use nothing more than barley water and yeast. You are allowed to use other grains but no additives or short cuts are permitted. The spirit must be aged in oak barrels for no less than three years and finally you cannot call your product Scotch whisky unless it has been made 100% in Scotland.
Bourbon is whisky made from a grain mixture which is at least 51% corn. Much like Scotch must be made in Scotland, Bourbon must be made in the United States.
Bourbon has no minimum aging period but to call your product Straight bourbon it must be aged for no less than two years in wooded barrels.