If someone learns English but they live in a non-English speaking country they are most likely learning English as a Foreign Language or FL. They do not need English for everyday survival and needs, but they will need it to conduct business or take an exam or when they are visiting abroad and so on.
For example, suppose a young girl in China wants to become a pilot. She will need to learn English in order to communicate with airports and ground crew around the world. She won’t need English to live in an English speaking country, and English won’t be her main language. So she will learn English as a Foreign Language.
Foreign Language vs Second Language
Compare this with the term Second Language which is English learned by someone who is actually living in an English speaking country. If the pilot above decides to move to the USA and live there permanently then she will need to speak English to interact in society on an everyday level. Thus she will use English as a second language.
EFL – English as a Foreign Language – English as a foreign language as oppose to a second language
ESL – English as a Second Language – English as a second language as oppose to a foreign language
TEFL – Teaching English as a Foreign Language – basic information about TEFL