off-roader vs all-terrain bike

off-roader and all-terrain bike both are nouns.

Word	Noun	Adjective	Verb	Adverb
off-roader	Yes	No	No	No
all-terrain bike	Yes	No	No	No

As nouns, off-roader and all-terrain bike are synonyms defined as:

off-roader and all-terrain bike: a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country

Other synonyms of off-roader include mountain bike.

off-roader (noun)	all-terrain bike (noun)
a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country	a bicycle with a sturdy frame and fat tires; originally designed for riding in mountainous country