A language that is not a person's native language/first language, but learned (for example in school) or acquired later (for example when a person moves to a different country where a different language is spoken). A second language can be a foreign language or another language used in that person's home country.
Sometimes, a distinction is made between English as a second language (ESL; English learned in countries where it holds a special status, for example as official language - i.e. in Nigeria) and English as a foreign language (EFL; English learned in countries where it is not the usual first language and where it does not hold a special status, i.e. in Germany).