"Les" is the French plural definite article, equivalent to "the" in English. It is used before plural nouns, regardless of gender, to specify particular items or groups. For example, in the phrase "les livres," it means "the books." In French grammar, "les" is essential for indicating that the speaker is referring to specific items known to both the speaker and listener. It is part of a broader system of articles in French, which includes singular forms like "le" for masculine nouns and "la" for feminine nouns, as well as the contracted form "l'" for nouns starting with a vowel.