It's all about how the heat is distributed. With convection and conventional ovens, they are powered by gas or electricity. But the heat source in a conventional oven just stays still, usually coming from the bottom, while in a convection oven a fan circulates the hot air around.
A convection oven has a fan that circulates the air within the oven that intensifies the heat and decreases the length of cook time. A regular oven is just a stove with no fan for circulation. They both are good for baking, roasting, heating, or drying foods.
The regular oven just heats the environment in which the food is placed. A convection oven heats the air that is then blown over the item to be cooked. The cooking process is faster with the convection oven.
A convection oven uses a fan to circulate heat evenly thoughout the oven, which in theory cooks more even and quicker than a regular oven. People I know that have one like it very much.
I think the huge difference is the price, with a convection oven costing $600 to $1000 more than a regular oven.
A convection oven has a fan that circulates the heat throughout the oven. It is much better than a regular oven for melting cheeses in meals like lasagne. A convection oven also cooks faster than a regular oven.
Both rely on heating elements. A regular oven relies almost only on radiant heat; a convection oven blows air around to distribute the heat more evenly.