In English, Castilian Spanish can mean the variety of Peninsular Spanish spoken in northern and central Spain, the standard form of Spanish, or Spanish from Spain in general. In Spanish, the term castellano (Castilian) can either refer to the Spanish language as a whole (to distinguish it from other Spanish languages such as Catalan, Basque, Galician, etc.), or to the medieval Old Spanish, a predecessor to Early Modern Spanish. Source: Wikipedia (en)