The part of speech that modifies a verb, adjective, or another adverb is an adverb. Adverbs commonly provide information about manner, time, place, frequency, or degree: in “she spoke quietly,” “quietly” modifies the verb “spoke.”
Many adverbs end in “-ly,” especially those formed from adjectives, such as “careful” becoming “carefully” and “rapid” becoming “rapidly.” However, the ending is only a useful clue, not a rule. Words such as “fast,” “often,” “very,” “well,” and “here” can also function as adverbs without the suffix.
Adverbs can modify adjectives, as in “extremely bright,” or other adverbs, as in “very quickly.” They may also modify an entire clause, as in “Fortunately, the rain stopped.” A common mix-up is confusing adverbs with adjectives: adjectives usually modify nouns, while adverbs modify verbs, adjectives, other adverbs, or sometimes whole clauses. Context determines a word’s grammatical role.