I see this listed on the server filters but I don't know what it is.
In Multiplayer Battlefield Bad Company 2, what is hardcore mode?
It is similar to call of duty's hardcore mode. Hardcore mode was added to further the sense of realism in the game.
In hardcore mode there is no HUD so you cant check how much ammo you have remaining etc, the amount of damage you can sustain is reduced so you'll be dead within a couple of shots, but watch out for those snipers! You will die within one shot from a sniper rifle. Finally there will be no kill cam so you can't see how you died.
I hope this info helps.
Differences between casual and hardcore: