The document discusses the rules for using the definite article "the" in English. It provides examples of when to use and not use "the" with different types of nouns. Some key uses include using "the" to refer to something already mentioned or assumed to be unique or known, and with names of geographical areas, decades, superlatives, and adjectives referring to groups of people. It is not used with uncountable nouns, names of individuals, countries, languages, or meals.