Piston
Piston Reset Speed, or just Piston Speed, is the time it takes for the piston to push the listed actions onto the action track.
The piston can have any speed from 1 second up in 0.5 sec steps. The speed is directly related to a build's weight - if no other speed affecting effects are active.
Builds under 400 kg have the fastest reset speed of 1 second, no action (right now) can go below that. Each additional 400 kg add 0.5 seconds to it. So builds between 801 and 1200 kg have a 2 sec reset time. And a 6050 kg build has a 8.5 sec speed etc.
Derived from the piston reset speed is the APM, actions per minute, rating.