Anaerobic means "without oxygen." Anaerobic bacteria, unlike humans, don't need oxygen to survive.
Aerobic means "needing or using oxygen." Think about aerobic activity, also called "cardio," like running, biking, or yes, taking an aerobics class at your local gym. That heart-pumping exercise makes your lungs take in more oxygen to keep you moving. Anaerobic is the opposite of aerobic. It means "without oxygen." Weight lifting is called an anaerobic exercise, because it doesn't require additional oxygen.