I'll add those to the script guide, I don't know why they're not in there (the script interpreter has them though). They're in the INI file though.
For an explanation on what they mean, this is from Google:
"The amount of time an axis takes to change its velocity from one velocity to another is a function of both Acceleration and Jerk. In physics, jerk is the rate of change of acceleration; more precisely, the derivative of acceleration with respect to time, the more quickly an axis will attain its programmed velocity."
In Skyscraper, the jerk rates smooth out the acceleration and made it more realistic.