The word aerobic is an adjective. Aerobic means (1) depending on free oxygen or air, (2) based on or using the principles of aerobics; enhancing respiratory and circulatory efficiency.
The following articles and web pages elaborate on the word aerobic.
Elliptical trainers provide a low-impact full-body cardiovascular workout. They are a popular choice for an indoor aerobic workout, but without the impact of jogging on a treadmill or pedaling a stair stepper.