Game mechanics

Your Character

 * Abilities - The strengths and weaknesses that define your characters, such as Strength and Intelligence.
 * Carrying capacity - How much weight your character can carry.
 * Classes - The role which your character will predominantly play.
 * Feats - Major new actions or advantages for your character.
 * Skills - How adept your character is at various tasks.
 * Enhancements - Minor new actions, advantages, and upgrades to your character's existing abilities.
 * Hit points - A finite value used to determine how much damage a character can withstand before dying.
 * Healing Amplification - Increases the amount of hit points restored when receiving healing spells or healing by other methods.
 * Run speed - How fast your character can run.
 * Player character conditions - Usually temporary, harmful and require certain actions to be taken to remove of them.

Attacking a Target

 * Attack bonus - Determines likelihood of hitting a target with melee or ranged weapons based on Base Attack Bonus and other modifiers.
 * Attack sequence - A chain of attack animations that depends on your character's Base Attack Bonus, fighting style, and whether you are stationary or moving.
 * Attack roll - Represents your attempt to strike your opponent.
 * Base Attack Bonus - Represents a character or monster's skill at fighting that comes purely from his or her profession, training, and personal experience.
 * Critical hit - A hit with an increased damage multiplier scored by rolling in the threat range on the d20 damage roll.
 * Critical hit multiplier - The number by which the base damage is multiplied upon a confirmed critical hit.
 * Damage - Damage reduces a target's current hit points.
 * Damage roll - Determines the amount of damage done after a successful attack roll.
 * Doublestrike - A chance to make an additional attack roll with the main hand weapon any time a main hand melee attack is made.
 * Fighting styles - The three main styles of melee fighting are sword and board, two-handed fighting and two weapon fighting.
 * Flanking - When attacking with a melee weapon, attackers receive a bonus for attacking from behind.
 * Grazing hit - Allows attacks to deal reduced damage instead of missing entirely if the total attack roll isn't enough to hit.
 * Glancing blow - An additional hit caused with a two-handed weapon that can strike multiple enemies. (Replaced by Strikethrough in Update 45.)
 * Melee special attack - A special attack that uses swings in the attack sequence to initiate a variety of single-target combat feats in addition to normal weapon damage.
 * Shield bashing - The act of attacking with a shield.
 * Sneak attack - Additional damage done by rogues under a specific set of circumstances.
 * Strikethrough - An additional hit caused with a two-handed weapon that can strike additional enemies.
 * Threat range - The range of the d20 damage roll where a critical hit can be scored. Actual range is determined by the weapon type of the attacker.
 * Weapon dice multiplier - A multiplier applied to the base damage die of particular weapons.
 * Vorpal Strike - Refers to rolling a natural 20, and confirming the critical hit.
 * Melee Power
 * Ranged Power

Defense

 * Active blocking - Produced by holding the block key. While blocking, a character gains +2 Armor Class, has increased DR, and is immune to most special attack and weapon effects.
 * Armor class - The likelihood you will be hit by melee and ranged weapons.
 * Armor check penalty - The skill penalties assessed for using armors.
 * Damage Reduction - Allows a certain amount of damage to be subtracted from each hit taken.
 * Dodge bonus - The chance of you completely bypassing physical attacks.
 * Guards - Effects that damage/debilitate your opponent as he attacks you.
 * Maximum dexterity bonus - The largest Armor Class bonus you can get from your Dexterity while wearing that armor.
 * Physical Resistance Rating - How much bludgeoning, piercing, or slashing damage is negated when you are hit.
 * Magical Resistance Rating
 * Saving throw - Chance to resist magical attacks
 * Spell resistance - Chance to avoid being affected by spells

Spellcasting

 * Casting ability - Different abilities benefit different spellcasters.
 * Arcane spell failure - The chance that an arcane spell will fail to be cast due to interference from the caster's armor or shield.
 * Spell - A spell is an activated magical effect produced directly by a creature.
 * Spell components - Spells have one or more components that are required in order to successfully cast them.
 * Spell critical - Percent chance for spells to score a critical hit. Base spell critical chance is 0%.
 * Spell Lore - Gives a bonus to your spell critical chance and increase the spell critical multiplier.
 * Spell point - The amount of magical energy your character has to expend on spells before needing to rest.
 * Spell Power - Determines how much damage you deal with spells.
 * Spell Resistance - An extra roll that the caster has to make for his magic to "land" on targets which possess it.
 * Spell-like ability - An ability that works exactly like a spell of the same name yet costs no (or very few) spell points.
 * Spell Penetration - Spell Penetration is the act of trying to penetrate Spell Resistance (SR).

Questing

 * Bravery Bonus - A special kind of experience point bonus which encourages players to run a larger variety of quests on harder difficulties.
 * Death - A condition brought about at -10 HP.
 * Death penalty - A temporary debuff on a character which was recently resurrected.
 * Dungeon Alert - A mechanic designed to reduce server load by limiting the number of enemies which can be safely handled by a party.
 * Dungeon Scaling - The mechanism that automatically adjusts the difficulty of quests depending on the number of players in the group.
 * Hireling - NPC adventurers that can aid you in quests.
 * Instance - A game area where players can encounter enemies or other players.
 * Quest - Adventures which reward xp and loot.
 * Epic (quest type)
 * Raid - A raid is a highly difficult and tactically challenging quest designed for 12 players.
 * Raid loot mechanic - The likelihood of receiving the item you want from a raid.
 * Raid timer - Most raids have a timer, or "cooldown" period, that starts after receiving end reward from the raid quest-giver NPC.
 * Ransack - Looting a chest too often within a certain span of time can temporarily reduce the quality and amount of treasure that chest generates for you.
 * Reaper - Reaper Difficulty or Reaper Mode is the highest difficulty in DDO introduced in Update 34.
 * Recall- A teleportation method available during a quest or while outside in a wilderness adventure area.
 * Repair (equipment) - Equipment can be damaged during questing and must be repaired at vendors.
 * Resource management - The process of managing finite resources (often spell points or clickies) throughout a quest.
 * Resting - The act of using a shrine.
 * Saga - A group of quests or even story arcs that characters can complete for an additional reward.
 * Sneak - Using Invisibility or creeping around using the Sneak toggle which relies on or your passive Hide and Move Silently skills.
 * Secret door - A door that appears to be an ordinary part of the wall, and can only be found by using special abilities.
 * Shrine - Monoliths found in quests that can be used to replenish hit points, spell points, and special abilities.
 * Social panel - An element of the UI used to help form parties.
 * Trap - Mechanical or magical effect built into a dungeon which are designed to impede the progress of the party.
 * Trapmaking - A feat made available to Rogues and Artificers that grants the ability to craft traps.

Monsters

 * Challenge rating - Relative danger of a monster.
 * Creature type - Defines features and traits for certain group of races.
 * Epic Ward - Epic enemies have massive amounts of experience against adventurers that form an Epic Ward against many attack types.
 * Monster attack bonus - A monster's bonus to attack rolls, helps determine the monster's likelihood of hitting you.

Leveling and Reincarnation

 * Action Point - Points gained in the process of increasing in level that are spent on enhancements.
 * Build point - Points spent to increase ability scores during the character creation process.
 * Class trainer - The NPC you speak to when you are ready to level your character.
 * Epic Destinies - A major part of an advancement system that players can use for their level 20+ characters.
 * Epic levels - An Epic level is not added to a class, but is a generic level in and of itself.
 * Experience points - Points earned via questing, which are required to level your character.
 * Experience points after Reincarnation(s) - Experience points required to level is increased after your True Reincarnation (TR).
 * Level - Can refer to many things: class level, Player Character level, caster level, spell level, or dungeon level.
 * Level cap - Level cap refers to the maximum Level a character can reach within a game.
 * Path - A predefined build intended for the use of inexperienced players.
 * Reincarnation - Allows players to change certain decisions made in their character's advancement or to create an all-new more powerful hero.
 * Respec - An MMO term that means re-specifying part or all of your character's current build.
 * Veteran Status - Allows you to start creating new characters at level 4 or level 7.

Dice Rolls

 * Ability check - A roll against an action's difficulty class, using an Ability modifier as a modifier.
 * Attack roll - Represents your attempt to strike your opponent.
 * D20 - Refers to a 20 sided dice.
 * Damage roll - This is the amount of damage that is done after a successful attack roll.
 * Difficulty class - A number associated with an action that represents how hard that action is to do.
 * Modifier - A number that changes a roll or a granted ability. It is usually tied to an ability score.
 * Natural 1 - A natural 1 is obtained when you roll 1 on the d20. On an attack roll or a saving throw, a natural 1 means a failure.
 * Natural 20 - A natural 20 is obtained when you roll 20 on the d20.
 * Skill check - A roll against an action's difficulty class, using a skill as a modifier.
 * Confirmation roll - A roll that is made to confirm a critical threat is a critical hit.
 * Vorpal Strike - Refers to rolling a natural 20, and confirming the critical hit.

Guilds

 * Guild Airships - A location where access is limited only to guild members or people who are temporarily invited.

Game Economy

 * Auction House - An automated way of buying and selling items with other players with in-game coin.
 * Base price modifier - Affects an item's price range and its minimum level requirement.
 * Bind - Definitions of various bind statuses of items.
 * Broker - A special type of vendor NPC which pays more for your items than other vendors do.
 * Currency - Usually refers to the in-game coin system, although other items are often used as currency by players.
 * Shard Exchange - A variant of the Auction House that uses Astral Shards as the only currency.
 * Daily Dice
 * DDO Point
 * Trade - directly between characters