TESOL stands for Teaching English to Speakers of Other Languages. It is the umbrella term for the whole field of teaching English to people whose first language is not English — anywhere, in any setting. It was created precisely because the older pair TESL (second language, learners inside an English-speaking country) and TEFL (foreign language, learners outside one) kept forcing teachers to pick a side, and the phrase 'speakers of other languages' quietly avoids that argument. So it is now the standard word for the profession as a whole: an MA in TESOL, a TESOL certificate, a TESOL conference. TESOL is also the name of the main international professional organisation, TESOL International Association, based in the United States, which publishes journals and runs a large annual conference — so 'she's presenting at TESOL' means the conference, not the subject. In Taiwan you will see it most on qualifications: a TESOL certificate is the usual thing a school asks for. It is pronounced as a word, 'TEE-soll' or 'TESS-ol'.