Passive means, in this context, that each unit is made of two sockets and a 50k linear potentiometer only.

There are no active parts like amplifiers or buffers and no power supply is required.
This is how the A-183-5 works: At the output socket appears the attenuated input signal, i.e. zero level at the fully CCW position and max. level and the fully CW position.

Applications:
Adjustable level of CV or audio signals to control other modules that do not have attenuators available.

Technical notes regarding modifications:

The document A183_5_modifications describes these modifications:

• normalling the inputs
• using the module as control voltage source (replacement for A-176)