Answer:
In depth knowledge and understanding of the language spoken (what is being listened to)
Step-by-step explanation:
In language (speaking and listening), the term L1 refers to a person's first language; it is the language which a person grew up with and is usually embraced naturally by a person as a child (up till around the age of 12). In some minor cases, a person can have 2 languages as L1 (in the case where a person was raised in a home setting where 2 different languages were spoken. For example, a house were English and Spanish were spoken, the child will have a bilingual L1).
L1 refers to the language one learnt without any 'significant effort'; it was just naturally picked up and it becomes like 'second nature' to the speaker or listener. L1 usually connotes that the speaker orlistener has an intrinsic & exhaustive knowledge of the language been spoken (when the speaker or listener is exposed to the lexicon, correct grammar, semantics, culture et al). L1 connotes that the listener has an in depth understanding of the language being spoken (understands content, etymology and context of what is being said)