This is a professional grade footswitch designed for heavy duty stage use by guitarists with big heavy feet!

3PDT stands for '3 Pole' 'Double Throw'.

'3 Pole' just means that there are 3 individual sides to the switch, for example, one side can be from your input socket, another to your output socket and another can be used to switch an LED on or off.

'Double throw' means that the switch moves from one tag to another. If using the wiring suggestion above, you can wire the input and output tags together on one set of tags, creating the True Bypass and the other would go to the circuit board, creating the 'on' setting.

Sounds a little complicated when written in words, but I can always send a diagram with the unit if needed.