I thought so (as an english-as-first-language), but I've met a bunch of people around the world who didn't know what ESL meant. I get the feeling the phrase is most known in American.
Well, my first wife was a schoolteacher, and my daughter is a schoolteacher. My second wife was a careers adviser. My son taught English as a second language for a while. So perhaps it's "trade jargon" that I have integrated.
