The phrase part of speech refers to an identifying label given to a word based on how it is used in a sentence.Although lists of these labels may differ slightly, grammar books traditionally list eight parts of speech:noun, pronoun, verb, adjective, adverb, conjunction, preposition, interjection.*
It is useful to understand why we bother with these classifications in the first place.In brief, having labels for how words function in a sentence helps us to understand better how sentences are constructed and therefore makes us more skillful at putting sentences together.