Parts of speech refer to the different categories into which words can be classified based on their grammatical function and meaning within a sentence. Each part of speech has unique characteristics that distinguish it from others and help to determine its role in a sentence. Nouns, for example, are words that represent people, places, things, or ideas, while verbs express actions, states of being, or occurrences. Adjectives provide descriptive information about nouns, and adverbs modify verbs, adjectives, or other adverbs. Pronouns replace nouns, prepositions show relationships between words, conjunctions join words or groups of words, and interjections express emotion or surprise. Understanding the different parts of speech is essential for effective communication and proper sentence construction.