A second language usually refers to a language that you learn in the country where that language is spoken. Immigrants coming to the U.S.A. and learning English would be learning English as a Second Language (ESL). A foreign language usually refers to a language that you learn where it is not the native tongue. For instance, a French student in the U.S. learning English would be learning English as a second language. A French student in France learning English is learning English as a foreign language (EFL). Some people prefer to call non-native languages taught in a classroom as world languages.