Twin-Linked
Twin-Linked weapons are a subtype of weapon found in the Warhammer 40,000 universe that embody a timeless tactic in warfare, why put all of your high velocity bullets/plasma rounds/freaky space mess in one basket when you can have two? The way this is done is typically duct taping two guns together and firing them at once so that the target has to avoid twice the number of rounds. Typically vehicles, monstrous creatures and terminators carry twin-linked weapons. They're called heavy weapons for a reason.
In Game Terms
When trying to hit a target you can reroll misses. This is useful, especially if you are using a weapon that is rather likely to melt your face off rather than fire at all, as it means that if you get a Gets Hot! result, you can reroll because it is a miss. Weapons that scatter get to reroll their scatter if they are twin-linked. This can be exploited to allow you to reroll ordinance (for example coupling a Triarch Stalker with a Doomsday Ark.