Aerobic means "With the presence of oxygen".
The term was made popular mainly by Dr. Kenneth Cooper, whose research in cardiovascular and exercise science showed that the human body could use several different energy pathways to efficiently perform exercise.
When faced with performing a moderate cardiovascular exercise for a sustained period of time, the body uses oxygen to breaks down our fat cells, converting it to a usable form of energy; the body then can continue performing the exercise with less effort than it would take by burning stored sugar, in the form of glycogen in our liver and muscles.
In truth, the body never depends on just one energy system and always uses a combination of fat and glycogen for most activities. However, the fat stored in our bodies can only be broken down with the presence of oxygen, and a higher percentage of it with rhythmic and sustained, moderate-effort activities, such as power walking…hence the term “Aerobic Exercise”.