TESOL stands for "Teaching English to Speakers of Other Languages". It refers to both ESL* (English as a Second Language) and EFL (English as a Foreign Language) instructors anywhere on the planet. I have a Masters in TESOL, for example, from the University of Kansas
ESL, too, can also refer to those who are teaching English as an L3, L4 or L5, etc.
In Japlish (Japanese English Slang), to TESOLing refers to the act of teaching Japanese: Weird phrases, like "Let's TESOL" then come into usage.