 ESL, English as a second language. ESL is a term that is commonly used in the USA, Australia and Canada. It is used in reference to non-native English speakers who use or study English in countries where it is the most commonly used language. It is also used to refer to the same situation in regions where the official language is English but other languages are more prevalent, such as former British colonial countries. This category of English language study and usage is often centered on migrant populations who choose to move to an English-speaking country as well as refugees who have fled from their own country and need to use English outside of their own ethnic communities.