Where is the diffenerce between EFL and ESL?

I would assume they are very similar; maybe they change the meaning slightly for 'correctness'?

EFL = teaching in a situation where learners are for the most part going to use the English as a Foreign Language. Most likely less frequently that if it were as a Second language.

As a teacher I have taught EFL and ESL both. In Korea and Indonesia I often taught/teach in EFL because my students would use English as a foreign language. For example Mr. Smith arrives in Korea and needs help finding a bus to his hotel the Korean providing directions in English speaks Korean about 99.99% of the time and his English is used rarely to help a foreigner find his way in Seoul.

On the other hand a Chinese student at my High School was learning ESL because he was required to use English as a Second language in classes conducted entirely in English.

So in some sense EFL is really the use of English in situations where English is considered a non-essential or foreign language. Where ESL is considered in use most of the time and is necessary to function. The same Korean moving to Los Angeles would probably consider his English to be a Second language not a foreign language since he would have to speak English almost everyday.

So really the difference for EFL and ESL is the location of the person and what he is being taught. A class can be ESL if the students intend on using the English on a frequent basis or EFL if they are going to remain in their country where English is not often used.