A flash hider is a part that goes on the end of a gun barrel. It reduces the bright flash that happens when a gun is fired by spreading out the gas. This helps hide the shooter’s location, especially in low light.
In relation to a suppressor, a flash hider can work with the suppressor to reduce both the flash and the noise. Some suppressors can even attach to the flash hider, making it easier to switch between using just the flash hider or adding the suppressor.