Here's why:
* It modifies adjectives or other adverbs: It tells us the degree or intensity of the word it describes. For example:
* "He is extremely tall." (Modifies the adjective "tall")
* "She ran extremely fast." (Modifies the adverb "fast")
* It doesn't act as a noun, pronoun, verb, adjective, or preposition: It's not a person, place, or thing (noun), a substitute for a noun (pronoun), an action word (verb), a word describing a noun (adjective), or a word showing location or relationship (preposition).
Let me know if you'd like to explore other parts of speech!