“Passing” refers to leaving your lane to go into something that either (1) isn’t a lane, or (2) is a lane traveling the other direction to overtake someone who is impeding traffic.

Moving into another lane that is going the same direction as you, such as on a freeway or road with many lanes, is not “passing”. It’s just changing lanes. You can go to the left or the right. True “passing” on the right is not legal.

The left lane is not a “passing lane” (in most states). It’s simply another lane. The laws in most states say that those impeding traffic must stay to the right. But most do not say anything about only passing in the left lane. The left lane is just another lane like any other lane in most states.