A STUDY ON
Halation is a characteristic of celluloid film when a bright light bounces back a few times exposing the film a second time only affecting the red layer (and a bit of the green layer) of the film resulting in a reddish/orange glow. The Halation tint may be different based on white balance adjustments / color grading.
An anti-halation layer usually is a coating on the back of the film base, though it is sometimes incorporated between the light-sensitive emulsion and the base. Its purpose is preventing any light from being reflected back through the emulsion from the rear surface of the base, or from anything behind the film. This prevents a halo-like effect (halation). Even with an anti halation-layer there might be a Halo effect because the layer is not 100% black.