Definition: Rewrite each original sentence in order to make it easier to understand by non-native speakers of English. You can do so by replacing complex words with simpler synonyms (i.e. paraphrasing), deleting unimportant information (i.e. compression), and/or splitting a long complex sentence into several simpler ones. The final simplified sentences need to be grammatical, fluent, and retain the main ideas of their original counterparts without altering their meanings.
Input: A first language (also mother tongue, native language, arterial language, or L1) is the language a human being learns from birth.

A first language is the language a human learns from birth. It is also called mother tongue, native language, arterial language, or L1.