Seriously, do they?! I think that it’s a fillet of pollock, but how can a fish have loins? Apparently, the manufacturers have taken to calling certain fillets that, probably in order to make it more palatable to consumers. Uh uh, not me. Fish is fish, and not pork loin chops. 
Well, if cod can have cheeks, why can’t pollocks have loins?
Picture holding a fish upright on its back, then slicing it from head to tail, and letting the halves fall apart. The skinnier, less meaty portion would be towards the outside edges of each half. Take the bones out of each side, and you have two fillets.
Trim off the less meaty outside portions of each fillet, and you have the loins. It’s a trimmed fillet.
If you’re familiar with beef tenderloin, think of a whole tenderloin with the “chain” trimmed off. Not exactly the same anatomically, but same idea.
The loin is the bit of flesh along the side of the body that extends from the lower ribs to the pelvis, and going back toward the spine.
If a fish can have a pelvis and ribs, I suppose it can have loins.
Beef loins are on the cow’s mid-lower back, so that’s not what people would consider the “loin” area either.
Let’s not even get into the issue of how a chicken can have breasts.
Before you cook the loins, you have to gird them first.