What unique aspect of nouns in Spanish is often noted?

Nouns in Spanish are often classified as either masculine or feminine, which is a unique aspect of the language compared to many others. This gender classification affects not only the nouns themselves but also the adjectives and articles used with them. For instance, the article "el" is used with masculine nouns, while "la" is used with feminine nouns. Understanding this gender system is crucial for proper agreement in sentences, as both the noun and any accompanying words must agree in gender. This concept is foundational in Spanish grammar, distinguishing it from languages that do not categorize nouns in this way. The presence of this gender system significantly influences language structure and sentence formation in Spanish.