Dynamic Shift, Dynamic Movement, Bump and Superscope all use several text boxes for code.  These are to seperate code so that different pieces of code can be processed at different times.  I'll explain the four types here:

Init:
The initializer box.  This gets processed at the very start of a preset (or when an effect is started) or whenever it's contents change.\

Beat:
This is only processed when Winamp detects a beat.

Frame:
This box is processed with every newly rendered frame.  If you have Wait for Retrace turned off (Options -> Windowed), this can conflict with the Pixel/Point box.

Pixel/Point:
This box is processed for every grid block, point, or pixel in the render.  In a superscope, it is processed n times and i increases by 1/n each time.