"London Dry is what most people think of when they think of gin. London Dry gins have to have all natural ingredients, and most importantly can't have any flavorings or colorings added (except for a minuscule amount of sugar) after the distillation process. London Dry is really a showcase for the botanicals.
"Distilled gin is made essentially the same way as London Dry, with one big difference—flavoring can be added after distillation. In recent years, as the perception of what gin can be has expanded, more distilled gins have hit the market, and some of them have become quite popular.
"Compound gin, or just plain 'gin,' can mostly be found—when it's found at all—on the bottom shelves at your local liquor store, and for good reason. There are no real laws governing how compound gin must be made, or what can or can't be added after distillation. Most compound gins have juniper flavoring infused after distillation, which makes it essentially a glorified flavored vodka. They're cheap, but you get what you pay for."