Important symbols

ESL (English as a second language),

ESOL (English for speakers of other languages),

EFL (English as a foreign language)

ELT (English language teaching)

TESL (teaching English as a second language),

TESOL (teaching English for speakers of other languages)

TEFL (teaching English as a foreign language) are all also used. 

EAL (English as an additional language),

ESD (English as a second dialect),

EIL (English as an international language), 

ELF (English as a lingua franca),

ESP (English for special purposes, or English for specific purposes),

EAP (English for academic purposes).

ELL (English language learner),

LEP (limited English proficiency)

CLD  (culturally and linguistically diverse).