#2 D usually refers to the more defensive oriented player who plays on the first pair. More often, instead of PP1 time, they are PK1, but often play heavy minutes 5V5 and on the PK. The league continues to evolve with basically all teams only playing one defender on the PP and so teams to deploy their most offensively capable Defender on PP1, many times it will be a specialist. a good example would be a guy like Adam Fox or Lane Hutson, who are adequate defenders but elite offensive defensemen. I would say that the modern prototype for a #2 D these days is probably a guy like Jaccob Slavin, though others on this board will obviously have differing opinions.