A positive image is a normal image.
A negative image is a tonal inversion of a positive image, in which light areas appear dark and vice versa.
A negative color image is additionally color reversed, with red areas appearing cyan, greens appearing magenta and blues appearing yellow.


What Photo Techniques can't describe, is the massive scripting by these comps (amongst some others):
The Olympian
ZeusMount_OlympusTheir names explain it all.