ESL is a common abbreviation used in schools and it stands for "English as a Second Language." Schools will often use the term ESL when describing the programs that educate students who are not native English speakers and for describing the 'ESL students' themselves.
Many schools will place children in an ESL program if their non-English speaking family recently immigrated to the United States or if a foreign exchange student needs extra help learning the language. It is designed to give these children special attention while learning English so they can integrate into a regular classroom.
The amount of time that a child will spend in an ESL program will depend on the child's grasp of the English language. For example, new students who know little or no English may spend most of the school day in an ESL class at first. Teachers will integrate the kids into a regular classroom as they become more proficient. On the other hand, students who understand and can speak basic English may begin with only an hour or two in an ESL program per day and spend the rest of the time in regular classes.