Castellano or Espanol?
Can anyone explain to me when spanish is called castellano and when espanol?
Castilian (Castellano) and Spanish (Español) are exactly the same language.
The Spanish language originated in Castilla region of Spain. The name given to the language originally was "castellano", not "español", because in Spain other languages were spoken with a number of speakers not much smaller than it (like Catalan, Basque, Galician, Asturian and Aragonese). With the centralization of the political power in Castilla, the Castilian language became the lingua franca (universal/ communication language) of the whole Spanish state, gradually replacing the other languages spoken, becoming "the Spanish language".
So, in some countries, this language is called "castellano" (like in Argentina, Paraguay and Chile) and some others call it "español" (like Mexico, Colombia and Cuba). In Spain, both are used, but "castellano" is the most used in bilingual regions, like Catalonia, Basque Country, Galicia, Valencia and the Balear Islands.
maybe this image can help you: http://moverdb.com/wp-content/uploads/Castellano-Espanol.png
Is the word «castellano» ever used to distinguish Spanish as spoken in Spain from Spanish as spoken in Latin America or elsewhere?
"Castellano" (Castilian) and "español" (Spanish) are synonymous. However, one of the spoken forms of this language is the Castilian Spanish/ European Spanish (español castellano/ español europeo/ castellano europeo), which is the Spanish/ Castilian spoken in Castilla (nowadays spoken in the whole Spain).
So there is the Castilian language (which is the same as the Spanish language) and the Castilian variety of the Spanish/ Castilian language.
So the answer is: yes, people can use "Castilian Spanish" to distinguish the Spanish spoken in Spain from the Spanish spoken in the American Continent, called (Latin) American Spanish.
Okay, so to say "I learned Castilian Spanish" — or "Spanish Spanish" as we sometimes facetiously say in the States— I would say, Aprendí español castellano. And you would know that I meant that I learned the language as spoken in Spain. ¿Verdad?
But then if I wanted to convey that I learned Spanish as spoken in the Americas, I might say, Aprendí español americano, ¿no?