An adverb is a word that modifies a verb, adjective, or other adverb. Adverbs answer how, when, where, or to what extent. They can appear in different positions in sentences. Many adverbs are formed by adding -ly to an adjective. Comparative adverbs end in -er or are formed with "more". Superlative adverbs end in -est or use "most". The document provides examples and exercises to illustrate adverbs.