Parts of speech are categories of words based on their grammatical function in a sentence. English has eight primary parts of speech:
1. Noun: Names a person, place, thing, or idea (e.g., dog, city, happiness).
2. Pronoun: Replaces a noun to avoid repetition (e.g., he, she, it, they).
3. Verb: Expresses action or state of being (e.g., run, is, think).
4. Adjective: Describes or modifies a noun (e.g., big, red, happy).
5. Adverb: Modifies a verb, adjective, or another adverb, often indicating manner, time, or extent (e.g., quickly, very, yesterday).
6. Preposition: Shows relationships between a noun/pronoun and other words, often indicating location or time (e.g., in, on, under).
7. Conjunction: Connects words, phrases, or clauses (e.g., and, but, because).
8. Interjection: Expresses emotion or surprise, often standing alone (e.g., wow, ouch).
Each part plays a specific role in sentence structure, and some words can function as multiple parts of speech depending on context (e.g., "run" as a verb or noun).