The lesson teaches students about the definite and indefinite article in English. It explains that the definite article "the" is used with specific or particular nouns, while the indefinite articles "a" and "an" are used with non-specific nouns or when introducing a noun. The lesson provides examples and rules for using articles correctly. It then engages students with a board game activity to practice applying articles and an evaluation exercise to assess understanding. The goal is to help students properly distinguish between definite and indefinite articles.