Spanish is the name of the official language of Spain. Within Spain it is spoken by about 40 million persons. Worldwide, approximately 500 million people speak Spanish as their native language, mainly in Spain's former colonies, and another 66 million people speak it as a second language. After Mandarin, it is the world's most spoken native language, and it is the third language (after English and Mandarin) most widely spoken in the world.
Within Spain, Spanish is most often referred to as "catellano," the language of Castile. Castellano is just one of several different paths taken by the Iberian provincial patois of Latin to evolve into modern speech. Other examples include Portuguese, which, by reason of its isolation along the Atlantic Coast, did not absorb so many Moorish words and terms as did Spanish, nor was it influenced by the language of the Visigoths when they conquered and settled in parts of Spain for centuries. Portuguese and its cousin, Galician, on the other hand did receive earlier influences from North Africa, when refugees from Carthage during the Punic Wars fled across into Iberia and stayed as far west as possible, to avoid the Roman legions. Catalan, by contrast, was heavily influenced by the Mediterranean culture around the port city of Barcelona, and by the languages of the neighboring French - Occitan and Gascon. Other Iberian language include Fala, Basque, Gascon-Aranese, Aragonese, Asturian, Caló and Extremaduran.
In 1479, when Ferdinand and Isabella married and then joined their kingdoms (Aragon and Castile), the alliance gave a new impulse to the centuries-long "reconquest" of Spain by Christian armies against the Moors. By 1492, under the "Catholic Monarchs," the expulsion of the Moors (and the Sephardic Jews) was complete. All the lands in Spain other than the Kingdom of Portugal, came under unified leadership. The mother tongue of Isabella of Castile, called "Castellano" (in English, "Castilian"), which had been the language of the court, now became the official language of the whole kingdom.
To this day, "Castellano" is the term used in Spain for "Spanish," especially when referring to the official language of the country, as contrasted to other languages spoken in the realm. "Español" is used to distinguish it from the languages of other countries. Elsewhere in the Spanish-speaking world, such as in Latin America and the Philippines, "castellano" is occasionally used as a term for the language, particularly as spoken in Spain, but it is much more common to hear the term "español."
Modern "castellano," spoken with a Castilian accent, is immediately distinguishable from any other kind of spoken Spanish. It is considered by those who speak it to be the prestige accent of Spanish, largely due to its long and influential history as the accent of the reigning nobility of Spain. Though Madrid (in New Castile) has been the national capital since 1561 (when Phillip II moved the throne from Seville) the origins of the Castilian accents are much older and come from much older towns in Old Castile -- Salamanca, Toledo and Segovia (the family home of Isabella herself). Apart from vocabulary choice, the Castilian version of Spanish is notable for the lisping of "z" and soft "c," a much more aspirated "j" and a slight muddying of the "s" to an "sh." In general, Castilian speakers form their words somewhat farther back in the mouth than other Spanish speakers.
By contrast, most of the troops who embarked for the new world after the successful reconquest were not from Castile, Leon or Aragon. They were from the south and west - provinces like Andalucía and Extremadura. They did not lisp their "z's" and soft "c's." They hissed their "s's" and only touched their "j's" lightly in the throat, if at all. These were the soldiers who were under the command of the conquistadores. They were the people who first colonized Spain's land claims in the New World. The Castilian accent was not an export of Spain to Latin America, except, perhaps in the highest social classes.
Spanish is spoken as the official language of 21 countries, and it is widely spoken in several others. The following are countries with significant Spanish-speaking populations: Canary Islands, Andorra, Argentina, Bolivia, Cayman Islands, Chile, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, El Salvador, Equatorial Guinea, Guatemala, Honduras, Mexico, Morocco, Netherlands Antilles and Aruba, Nicaragua, Panama, Paraguay, Peru, Philippines, Puerto Rico, Trinidad and Tobago, U.S. Virgin Islands, Uruguay, and Venezuela. The largest Spanish-speaking population is in Mexico. It is the second most widely-spoken language of the United States. It is the third most common language of the Internet, after English and Chinese. Spanish is also one of the six official languages of the United Nations, an official language of the European Union, and of the Organization of American States.
Spanish is an Indo-European language, derived from Latin, and considered one of the principal Romance languages. It has a high degree of similarity with other West-Iberian Romance languages, such as Portuguese, with which it shares an estimated 89% "lexical similarity." Portuguese pronunciation makes it difficult for a Spanish-speaker to understand it, but the reverse is usually not true. Spanish is also similar to Italian, with which it shares an approximate 82% of lexical similarity. The indices for French (75%) and Romanian (71%) are much lower, and the pronunciation differences make them mutually unintelligible with Spanish, especially for persons who have not studied the other tongues.
The grammar of Spanish is similar to that of the other West Iberian dialects, but has been considerably simplified over Galician, Portuguese and Ladino. (Ladino is a post-medieval dialect of Spanish still spoken by Sephardic Jews who were expelled during the "reconquest" and settled in Turkey, Greece, the Balkans and now in Israel.)