two basic types of scotch whiskey, a single malt and blended. Single is preffered. Every maker has their own technique but to be true scotch the malt is smoked or roasted with burning peat. it is aged in barrels, the type of wood and duration varies but as stated above the age is considered time in barrel. and reflects the amount of flavoring it absorbs from the barrel or cask.
A relative new commer to the scene is vatted whisky which some call a scotch. it is a result of high production levels. I believe chivas is a vatted scotch. basically it is a mix of single malt scotches.
I think that it has become common to call almost all finer whiskey scotch no matter what the grain used but real scotch is made from a barely malt.