Active/Tru-bypass Switching - With Active Switching, when the Distortion and Boost circuits are turned off, the audio signal is passed through using "transparent" electronic buffers. With Tru-bypass Switching, when the box is switched off,  the audio signal is passed through  using mechanical switch contacts - "absolutely transparent". The latter have a classic look and feel which is preferred by some, whereas the Active Switches have a modern look and feel.