Spanish (or Castilian, castellano) is a language which developed from a relatively early form of Latin (earlier than the varieties which developed into Catalan, Italian or French), with a Celtic substratum and Germanic and Arabic superstrata as a result of the subsequent invasions by the Visigoths and Arabs respectively. The many varieties of Spanish spoken in the Americas also show influences from native American languages and in some places (particularly Colombia and Argentina) from Italian as a result of substantial Italian emigration in the late 19th and early 20th centuries.
The result of centuries of Spanish colonialism is that it is one of the world's most widely used languages, with around 350 million native speakers, in the same ball park as English and Hindi and only significantly surpassed by Mandarin. It is an official language in 21 countries and widely spoken in as many more, and is a working language of the United Nations. The Real Academia Española, a Spanish body with international connections, has some notional authority over the language, but its real influence is limited.