English as a second language (ESL), English for speakers of other languages (ESOL) and English as a foreign language (EFL) all refer to the use or study of English by speakers with different native languages. The precise usage, including the different use of the terms ESL and ESOL in different countries, is described below. These terms are most commonly used in relation to teaching and learning English, but they may also be used in relation to demographic information.

English language teaching (ELT) is a widely used teacher-centred term, as in the English language teaching divisions of large publishing houses, ELT training, etc. Teaching English as a second language (TESL), teaching English to speakers of other languages (TESOL) and teaching English as a foreign language (TEFL) are also used.

Other terms used in this field include English as an additional language (EAL), English as an international language (EIL), English as a lingua franca (ELF), English for special purposes, or English for specific purposes (ESP), English for academic purposes (EAP). Some terms that refer to those who are learning English are English language learner (ELL), limited English proficiency (LEP) and culturally and linguistically diverse (CLD).