what's 'Active preamp' vs 'Passive preamp'?

The general definition of 'active' and passive' is similar to the audiophile definition.

Passive components are resistors, capacitors inductors and transformers, none of which requires a power supply in order to function. Passive preamps are made of these devices.

Active devices include transistors, integrated circuits and vacuum tubes (among other things) require a source of AC or DC power in order to function and their inclusion in active preamps is what is indicated by the AC cord.

Transformers can add voltage (gain) but only at the expense of current and add current (gain) at the expense of voltage. Because they are passive, no net increase in energy is possible.

Kal