Conventional ovens draw their heat from a stationary source, generally up from the bottom, and they can either be powered by gas or electricity. A convection oven, on the other hand, uses a fan to move heated air around the oven.
Convection ovens cook food quickly and evenly, as the temperature is more consistent within the entire space of the unit. However, both gas and electric conventional ovens can feature pockets of air at different temperatures. Heat tends to rise, so if food is being prepared on both racks, the higher dish can burn while the lower dish does not cook sufficiently.