PAS stands for Pedal Assist or Pedelec and is a mode that provides power only when you are pedaling. If you are used to riding a traditional bike, the pedal assist mode has a more intuitive feel compared to the throttle mode.
A lot of pedal assist bikes have different levels of assistance, for example: low, medium, or high assist. Please note that some e-bikes have 4 or 5 pedal assist settings, but for this example we will just stick with low, medium, and high.
Low pedal assist = you are feeling pretty good on the bike. Low assist provides a little electric assist while you provide more pedal power and get more of a workout.
Medium pedal assist = you have a nice tailwind everywhere you go. Medium pedal assist can be a nice balance of your pedal power and the motor power.
High pedal assist = you feel like superman! High pedal assist is when you want to get somewhere quickly and with minimal effort. This could be useful if you want to get to work without sweating too much. On the way home you could use the low pedal assist to workout the stress of the day.