Joke Collection Website - Bulletin headlines - What do source language (SL) and target language (TL) mean?

What do source language (SL) and target language (TL) mean?

source language (SL) source language (the language originally used)

target language (TL) target language (the language to be changed)

For example: when translating from Chinese to English, SL is Chinese and TL is English; when translating from English to French, English is SL and French is TL