IFF or Identify Friend or Foe is the term used for a person of being to figure out what to do with an enemy or a friend. This is not uncommon in auto-defenses and targeting systems and such will only open fire on those not in it's 'Friend' database. Usually staff at a facility are registered to the facility's network are added to the IFF database to all defenses within it.
The IFF systems in Perfect Dark are found in AutoGuns, Robots and Tracking systems in some firearms.
So visually simplified, especially on counter-operative mode, when a Autogun spots the player working against the 'Jo' player, it will not turn to attack, but if the 'Jo' player is spotted by the gun, it will open fire upon him/her. Also, the aiming reticule will turn blue when targeting a neutral/friendly or red when targeting an enemy.
Perfect Dark's combat simulator hints extensive flexibility of the IFF system in the Laptop Gun, when players and simulants are shuffled in a team and one of the team-members throws a wallgun or uses a tracking system in a firearm then it will ignore all other team-members, even if some were originally in a different team.