Passive means there is nothing done to the signal that comes from the pickup. The only change is from the knobs that are on the bass. Which are just filter circuits that as you turn the know allow only a certain range of frequencies to pass. Example: Bass knob. This will filter out a range of high frequencies so as you turn the knob the circuit bleeds off the highs and leaves the lows.
Active means there is something done to the signal before it passes through knobs. Mainly, some amplification. Makes the signal a little stronger before it eventually leaves the guitar and into the amp. Usually, on the good setups they strip off some of the noise etc, that might happen to get into the signal from the pickups...
BassFool.....