Q:

Technical term for aural proficiency in a language

I have encountered several individuals in the past who have a certain level of proficiency and understanding in listening to a certain language, but are on the whole unable to create and speak/write in that same language. 
Often times, these individuals grew up in an environment where said language was spoken and used-- and as a consequence learned to understand the tongue-- but communicated outside of the home using an altogether different language. 
I understand that reproducing a language on your own is entirely different from understanding, or translating something spoken to you, but have always been curious if this is a more widely documented phenomena regarding language learning. 

A:

TL;DR Passive speaker

You've probably seen something like this before,

+-----------------+-----------+------------+
| LANGUAGE SKILLS | RECEPTIVE | PRODUCTIVE |
+-----------------+-----------+------------+
|                 |           |            |
| Auditory        | Listening | Speaking   |
|                 |           |            |
| Textual         | Reading   | Writing    |
+-----------------+-----------+------------+

representing the four major areas of language learning (listening, speaking, reading, writing) and how they relate to each other. Receptive (more passive) skills are those involving language experienced (by the learner), and productive (more active) skills are those involving language expressed (by others).
Receptive skill proficiency naturally precedes productive skill proficiency because

Well, the only way to learn new words is through a receptive method (unless you're making up words), so since they enter the vocabulary through a receptive method, it makes sense that comprehension would naturally be strongest there.
When reading or listening, words are almost always in a specific context, and meaning can be much easier derived from it, as opposed to when attempting to recall a word, when context (aside from experience with the word) is not available.

Proficiency in receptive areas can be called receptive (language) competency or passive knowledge, and those exhibiting this characteristic are called passive speakers:

A passive speaker (also referred to as a receptive bilingual or passive bilingual) is someone who has had enough exposure to a language in childhood to have a native-like comprehension of it, but has little or no active command of it.

Note: The term "passive speaker" also includes reading comprehension.

Here's another useful link on passive vs active vocabulary.

