This question asks about the grammatical category (la nature) of the word rapide.
Rapide is an adjectif (adjective). An adjective is a word that describes or qualifies a noun. Rapide means "fast" or "quick" and is used to describe nouns, for example: une voiture rapide (a fast car), un train rapide (a fast train).
It does not belong to any of the other categories:
A nom (noun) names a person, place, thing, or idea (e.g., la vitesse - speed)
An adverbe (adverb) modifies a verb, adjective, or another adverb. The adverb form of rapide is rapidement (quickly), formed by adding -ment to the feminine adjective
A verbe (verb) expresses an action or state (e.g., courir - to run)
A common mistake is confusing rapide (adjective) with rapidement (adverb). In French, most adverbs derived from adjectives end in -ment.
