Yep, more precisely rapidfire is the avarage number of shots your ship takes against another one in one round.
So if let say a battlecruiser has rapidfire 7 against battleship while the battleship hits the battlecruiser once, the battlecruiser will hit the battleship 7 (on average, could be more or less) times, or if the battleship it was attackin is destroyed, move on to the next target with its next shot.
When you have rapidfire 7 there is like a %90+ chance that your ship will fire again after each time it fires.
Basically rapidfire is amazing
Battlecruisers only have a base attack of 700 compared to battleships 1000 but they kill battleships nearly at a 1:2 ratio