ESL is English which is usually taught to students in an English speaking country. EFL is English which is taught to students in a foreign, non-English speaking country. As it is true of many European countries, where is common to learn to speak more than one foreign language. For these reasons ESL is typically the term used in the United States, an English-speaking nation, whereas EFL is more often the term of choice in countries where English is not the native language.
TEFL stands for Teaching English as a Foreign Language, and traditionally refers to teaching in non-English speaking countries. TESL stands for Teaching English as a Second Language and refers to teaching in English speaking countries, to non-native speakers living or working there.
In practice, the acronyms TEFL and TESL are often used interchangeably, and both are covered by the all-encompassing TESOL, which stands for Teaching English to Speakers of Other Languages.
以上為TEFL和TESOL之間的專業解釋，從中我們可以看出，TESOL其實是包含兩層含義的，一個是針對英語為非母語國家的人進行教學，一個是針對英語為母語國家的人進行教學，而TEFL是針對英語為非母語國家的人進行教學。至此其實有些問題就比較好理解了。
1，在英語為非母語國家，TESOL資格證書（international TESOL certificate）和TEFL證書是一樣的，沒有概念上的區別，功能和效力是一樣的，可能唯一的區別是認證機構的課程體系設置以及頒發證書的機構。
2，TESOL學歷類的證書一般來說是可以在英語為母語國家使用的，如果美國，澳大利亞的很多機構或者學校在招聘老師的時候，會有相應的TESOL學歷要求。
3，TEFL更多是指一個行業，而TESOL是指一個專業學科。
可見，在我們國內使用的國際英語教師資格證書，TEFL證書和TESOL證書是沒有區別的，二者都是等同對待，這就是為什麼往往會標示為TEFL/TESOL證書。