A GunFlash

A_GunFlash is a code pointer used in the attack animation for the BFG 9000 and Rocket Launcher.

Uses
The  code pointer appears in the following states in Doom's state table:

Example
The following is an example of how to set the  code pointer in a Dehacked file:

Pointer 21 (Frame 34) Codep Frame = 85

Or using BEX syntax:

[CODEPTR] Frame 1234 = GunFlash