"Οι" is a Greek article that translates to "the" in English. It is used to indicate a specific noun and is typically used with plural nouns. For example, in Greek, "οι άνθρωποι" means "the people." The article agrees in gender and number with the noun it modifies. In Greek grammar, "οι" is the plural form of the definite article for masculine nouns. It is essential for sentence structure and clarity, helping to specify which particular group or individuals are being referred to. Understanding its use is crucial for anyone learning the Greek language.