ESL is used to indicate that English is not the first language that the individual has learned or uses as their first or native language. In fact for many language students English may be their third, fourth or fifth language. The term ESL is used to indicate that English is not the native language of the individual.
Many ESL teachers will refer to the individual's native language as "L1" and English as "L2" or the "target" language.
Individuals who are studying English as a second language can state "I am an ESL student" or "I am a student studying ESL" or use the full English words and state " I am studying English as a second language".
Individuals can clarify themselves by stating I am studying English as a foreign language, which for many means that you are studying English as an academic subject and do not plan to use English for actual communication. Individuals can also clarify themselves by stating that they are studying English Literature which is like the history of English Performance Art and do not plan to use English for actual communication.
ESL students usually study English Language listening, speaking, reading, writing, grammar and vocabulary to be able to actively produce English conversation and writing and passively comprehend verbal and written English. The ESL students usually study in an interactive learning environment where they are provided with instructional input and are expected to produce both learned and original English language communication.