aerobic exercise vs aerobics

aerobic exercise and aerobics both are nouns.

Word	Noun	Adjective	Verb	Adverb
aerobic exercise	Yes	No	No	No
aerobics	Yes	No	No	No

As nouns, aerobic exercise and aerobics are synonyms defined as:

aerobic exercise and aerobics: exercise that increases the need for oxygen

aerobic exercise (noun)	aerobics (noun)
exercise that increases the need for oxygen	exercise that increases the need for oxygen