Abbreviations

There are many different abbreviations used in DotD, here is a list of the most commonly used.
*AP - Can mean either Achievement Points or describe the amount of damage needed to get Achievement Points. eg Half of Fair Share gives AP or you need X amount of damage for AP.
*BSI - Battle Strength Index is the measure of the Stat Points you have spent on attack and defense. (BSI = (Base Attack + Base Defense) / lvl) 
*FS - Fair Share is the minimum amount of damage each player in a raid would need to do to complete the raid. Fair Share is calculated by Raid Health divided by max amount of players that can join the raid.
*MS/ME - Max Share or Max Epics is the highest tier on a raid
*OS - Optimal Share which is the optimal amount of damage to do to a raid to receive the most Stat Points for the damage done.
*TSI - Total Skill Index is a measure of all Stat Points spent. TSI = (Base Attack + Base Defense + Base Perception + Base Energy + Base Stamina*2 + Base Health/5) / Level