Question about something in my chat

[Niwashi]

when I'm attacking a mob, next to their name is a letter like in N or Z what does that mean?

It's just a way of distinguishing between multiple mobs of the same type. You could, for example, refer to "Opo-opo N" rather than "the one over there, to your right, next to the big guy" or whatever. (It's seldom, if ever, useful.)

More commonly, if you want to refer to a specific mob when talking to others in your party, you'd place a marker (main menu -> party -> signs) on the mob. The most common use is to indicate which mob to attack first or (more rarely) which to leave alone. In that case, you generally don't even need to talk about it, just use the "Target to Attack 1" "Target to Attack 2" and so on signs to let people know the attacking priorities, or "Target to Ignore 1" "Target to Ignore 2" and so on if you want to indicate that mob shouldn't be attacked yet. These signs will be visible to everyone in your party.

[Frizze]

It's just a way of distinguishing between multiple mobs of the same type. You could, for example, refer to "Opo-opo N" rather than "the one over there, to your right, next to the big guy" or whatever. (It's seldom, if ever, useful.)

Emphasis mine. My understanding is that its part of the UI that numbers the mobs(well, letters them but you get the idea) so that you can tell them apart at a glance(if you look closely). In my experience, the "numbering" on your screen wont always be the same as that on your teammates screens. So, "seldom if ever useful" sums it up.