Reserved global variables are variables to which MAXScript automatically assigns values. The MAXScript reserved global variables fall in 3 categories: predefined globals (such as red and pi); 3ds Max system globals which give you access to state information in the 3ds Max system (such as currentFrame); and MAXScript system globals which give you access to the MAXScript system state.
Unlike language reserved keywords, you can re-use these variable names as local variables, with values that you specify. However, it is highly recommended that you do not re-use reserved global variable names as such usage can be highly confusing.
3ds Max System Globals
MAXScript System Globals
Variables - Assignment and Scope