In most grammar books you will find the definition of simple adverbs and derived adverbs. Derived adverbs are the ones that are formed with a pre- or a suffix. For instance most English adverbs are derived, they are adjectives + ending -ly. Further, there are mostly also some simple adverbs. They are words that can only be used as adverbs or, they are words that are identical with the adjective. Which again means, that some adjectives can not be used to form derived adverbs.