Usually housed in a 1U rack-mountable metal chassis for heat dissipation. Active Joining:

The terms "12 serial" and "amp" (amplifier) suggest professional rack-mount hardware used for signal distribution: ThinkCentre neo 50t - Lenovo PSREF

Long cable runs act like antennas, picking up electromagnetic interference.

The phrase most commonly refers to a specific software utility by ManiacTools used for editing audio files by cutting (splitting) and merging (joining) them. The reference to "12" likely refers to the software's latest major version, v12.0 . Alternatively, in a hardware context, a " 12 Way Video Audio AMP Splitter

Splitting microphone signals so they can be sent to both a live mixer and a recording interface simultaneously.

Splitting a primary camera feed to multiple monitoring stations. Broadcast: