English grammar
Adverbs are words that tell you about words that are not nouns.  An adverb can describe a verb, like the word "quickly" in the sentence "He ran quickly."  They can also describe an adjective.  The adverb "very" describes the adjective "sick" in the sentence "The boy is very sick." Adverbs can even describe other adverbs, as in the sentence "He ran very quickly."