An ELT Glossary : ELT /TESOL

ELT : English Language Teaching (used especially in Britain)
TESOL : Teaching English to Speakers of Other Languages (used especially in the US)

These two acronyms are used as "umbrella" terms to refer to any situation in which English is taught to learners with a different first language, regardless of whether they are it as a foreign language, as a second language, for specific purposes or whatever.