There are eight parts of speech in English: noun, pronoun, verb, adjective, adverb, preposition, conjunction, and interjection. Understanding parts of speech is essential for determining a word's definition and how it functions grammatically within a sentence. Each part of speech has a specific grammatical function, such as nouns naming people, places, or things, verbs expressing actions or states of being, and adjectives describing nouns. A word can sometimes function as different parts of speech depending on how it is used in context.