Terminology. Why does it bug me and others?

[Razzle]

I thought DD meand Damage Dealer, as in a class/job who's role is to... Deal damage hehe...

While DPS means Damage Per Second, which is basically means the amount of damage you deal over time.
The term DPS can be used on any job or class. Example: A WHM spamming stone is DPSing for X.

While DD can not. A WHM is not a DD(it's main role isn't dealing damage), but can DPS using damage dealing spells.