Too many people overcomplicate the idea of smoked barbecue. In reality a smoker is a big oven that you cook with that produces beautiful, flavorful smoke. This smoke is absorbed into your meat and becomes a unique category of cuisine.
Even though many outdoor cooking methods can produce smoke that gets absorbed in the meat as flavor, smokers are intended to envelop the meat in smoke for a sustained period of time in the beginning thereby getting the maximum flavor infused into the meat.
Smoke is the primary difference
Unlike other cooking methods, barbecue is almost always accompanied by smoke. This was at first a by product of the method hundreds of years ago when people would drop a large piece of meat into a pit on top of and surrounded by coals and then cover it over. As the meat slowly cooked, the smoke was trapped and ended up permeating the beef or pork.
As people began to build ovens in the same fashion, they tended to make them enclosed to produce the same effect. Nowadays, smokers are manufactured in a wide variety of types and a range of fuels.
How a smoker works
The basic principle is quite simple. You need an air intake in the bottom and a wood product to burn that creates smoke that swirls around the meat and exits through a vent higher up.
Since heat rises, it creates a natural flow entering and exiting.
By opening the lower and upper vents, you allow more oxygen to flow through and this will create more heat and smoke.