What does it mean when I unlock carbines in BF4?

I was playing as an engineer in Battlefield 4 last night, and was awarded a "Carbine" unlock. What does that mean? Did I unlock the carbine class of weapons, or just a particular carbine gun?

For example, looking in Battlelog > Profile > Unlocks > Weapons, I see a grid of carbines where one carbine has an orange bar under it, and one carbine has half an orange bar. Is the one with the full orange bar the one I unlocked?

I find the documentation and user interface confusing, as I am new to FPS games.

What you unlocked was a new section of guns that you can unlock. I highly suggest using them as they are some of the most powerful guns in the game. These can be used on any class making them a good set of weapons to get used to using. The orange bar is the progession through the weapon class. Its basically an xp bar, so when you "level up" you get another gun in that section! The gun with the orange bar that is full under it is the gun that you have unlocked to use currently, as you get more kills or assists (points) with the carbines the other orange bar will progress and eventually unlock the other guns, so like I said before "leveling up".

The way you progress with primary weapons in BF4 is by using them (with the exception of those you unlock thorough assigments). So the more you use a carbine, the more points get to unlock the next one(s). For example, I used the ACW-R a lot before I unlocked the ACE 52 (and I've used it as my primary weapon for the three kits that can carry a carbine, it is an excellent gun). The more you play with the gun means the more attatchements you unlock with them as well (apart from the ones you get through battlepacks).