What is convection?
Simply put, a convection oven has a fan and an exhaust system, while a regular oven does not. The fan and exhaust system help blow hot air around the food and then expel it. Therefore, the hot air surrounds the food, making it cook more evenly and faster.
A good way to describe this from fine cooking: "To help understand this, think of wind chill: when a cold draft blows on you on a windy winter day, you feel colder faster than on a windless day at the same temperature." The same applies to heat and convection cooking!
Why use convection?
It cooks faster: Because the hot air blows directly onto the food, rather than just surrounding it, food cooks about 25% faster in a convection oven. It cooks more evenly: A regular oven can have hot spots depending on the location of the heating elements, but the fan in a convection oven circulates air to help even out temperature differences. Browning is better: The air in a regular oven can become a bit humid because moisture cannot escape. Convection creates a dry atmosphere, causing caramelization to occur more quickly during baking, resulting in meats and vegetables browning more rapidly while remaining moist inside. It also saves energy: because food cooks faster and at generally lower temperatures in a convection oven, it is more energy efficient than a conventional oven.