You may have heard reference to Castellano, or Castilian, Spanish. This is something which often causes confusion amongst students and prospective students of the language. Is there a difference?
Spanish, as you may already know, has several variants which grew up out of the Latin language around 2,000 years ago. Today, some of these dialects, like Andalusian, Catalan, Galician and Basque (or Euskara) still survive and are official languages in the autonomous regions in which they are spoken. Castilian or Castellano, however, is the official form of the language as standardised in the 13th century by King Alfonso and regulated by the Royal Spanish Academy to this day. It is known as Castilian because it originated in the north-central region of Spain which includes Castile, but after it became the official language of government, it spread throughout the country and indeed to Latin American Spanish-speaking countries too.
Nowadays, Castellano and Español are effectively interchangeable terms. The name Castellano is generally used only to differentiate the ‘pure’ Spanish from these other dialects which are, after all, still undeniably Spanish. The Spanish Constitution of 1978 enshrines Castellano as the official language of the state, and so whether somebody refers to it as Spanish or Castilian is often simply a matter of personal, regional or political preference. As a learner, all you need to know is that Castellano is the ‘mainstream’ form of the language which has the highest number of speakers around the globe and which we teach in all of our Spanish language courses. So there’s no need to feel daunted or imagine you need to master different versions of the language as Castellano is spoken and understood right across the Spanish-speaking world.