This command ignites your character (setting you on fire), but you do not take damage. You can set fire to other flammable objects/entities by colliding with them (e.g. jumping on them).
The syntax for the burn command is as follows:
burn
Search our database of 116 Left 4 Dead 2 commands...
Yes PleaseFind below working examples of the burn command.
burn
This is the only way to use the burn command. Typing this into the console will set you on fire.