The tank has more than one turret. For every rating, it gains one additional turret. These turrets are not armed with a weapon by default, but can be equipped with one or more weapons.
The tank may make more than one shooting interaction per turn - one per armed turret. It chooses which turret(s) to use. These interactions are an exception to the rule of picking only one target. Each shooting interaction can have its own target, but the accuracy decreases: The shooting tank has to roll To Hit separately for every turret (but only once for all the turret's weapons combined), and adds 1 to the TN for hitting any target except the first.
The maximum number of shooting interactions per turn, regardless of the number of turrets, is the tank's Buf score or Interaction Pool (whichever is lower).