The document discusses parts of speech, defining them as the categories that words are classified into according to their function in sentences. It notes that in traditional grammar, these categories were called parts of speech, while in contemporary linguistics they are referred to as word classes. There are eight main parts of speech in English: nouns, pronouns, verbs, adjectives, adverbs, prepositions, conjunctions, and interjections. The document encourages learning parts of speech by making a poster that illustrates the eight categories and their functions.