"Los" is a Spanish word that translates to "the" in English, used to refer to plural masculine nouns. It is a definite article, indicating specific items or groups. For example, in the phrase "los libros," it means "the books." In Spanish grammar, articles like "los" agree in gender and number with the nouns they modify. This means that "los" is used with masculine plural nouns, while "las" is used for feminine plural nouns. Understanding the use of "los" is essential for proper sentence structure in the Spanish language.