EFL is an abbreviation for "English as a Foreign Language". This is mainly used to talk about students (whose first language is not English) learning English while living in their own country. (For example, a Chinese person learning English in China.)
ESL is an abbreviation for "English as a Second Language". This is mainly used to talk about foreign students learning English while living in an English-speaking country. (For example, a Chinese person learning English in Canada.)
Other expressions that people use are ESOL (English for Speakers of Other Languages) and EAL (English as an Additional Language).
We also use the terms:
- TEFL (Teaching English as a Foreign Language)
TESL (Teaching English as a Second Language).
TESOL (Teaching English to Speakers of Other Languages)