 TESIL stands for Teaching English to speakers of overseas or other languages and TEFL stands for Teaching English as a foreign language. Both terms are used interchangeably, so going back when the industry first developed, TEFL was more of a UK based qualification and TESIL was more of a North American based qualification. As the industries developed the two terms of use interchangeably, so the acronyms TEFL and TESIL are used to describe the English language teaching industry. There are also acronyms that will appear on your certification at the end of the course as well.