Old Spanish, also known as Old Castilian, refers to the early form of the Spanish language spoken from the 10th to the 15th centuries. It evolved from Vulgar Latin and was influenced by Arabic due to the Moorish presence in the Iberian Peninsula. This period saw the development of distinct regional dialects and the emergence of a standardized written form. The language underwent significant changes during the Renaissance, leading to the transition to Modern Spanish. Old Spanish featured different grammar, vocabulary, and pronunciation compared to contemporary Spanish, making it a fascinating subject for linguists and historians studying the evolution of the language.