Found the answer in: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2281820631

"You'll notice that there are different firing types. All ranged weapons have aimed fire, snapshot fire, and supressive fire.

Aimed is basically the default.

Snapshot shoots faster, but with less accuracy.

Supressive fire works like snapshot, but will still fire at enemies even if they're supressed or 'hunkered down'."

Aimed Shot has the shooter take a bit more time to aim, reducing the impact of weapon sway. This is good for precision weapons or at longer ranges. Sway is also reduced as the shooters' Shooting skill improves.

Snapshot is a bit quicker, and can be preferable at closer ranges.

Suppress is identical to Snapshot, but will not interrupt the burst if the shooter loses sight of the target. This can be good for keeping peoples' heads down as they're popping in an out of cover.