RPG Terms

D# – Dice sizes
A D4 is 4 sided. Used for magic missile. If we had a cleric, that person could cast Bless on the party and allow us to roll an extra D4 on attack rolls and saving throws.
D6 is 6 sided, D8 is eight sided
D10s are also called percentile dice. One of the dice is a regular D10 (numbers 1 through 0 – the 0 being the 10) and the other die having 10 through 00 (00 being 100). D12s are what mighty, and massive half-orc barbarians get to use for hit dice.
The D20 is the dice used for “deciding whether something happens or not”. You roll the 20 to attack, for saves, and for skill checks. Depending on the situation and the requirements set by the DM the number rolled determines whether or not you are successful with your chosen action.

Class
Your class in D&D can be thought of “what you do” in your fantasy adventure.

Race
Your race is your identity. Adventurers get bonuses based on which race they choose.

PC/NPC
Player Character (the adventurer)/ Non-Player Character (people the DM/GM creates to interact with, or be killed by, the mighty adventurers.

Attributes/Skills
Your skills are how well you perform different acts. Your chosen class and race will give you different skills you can be proficient in. Half-orcs are naturally proficient in Intimidation–which is Charisma based– so Gozer gets to add her proficiency bonus to her Charisma modifier for a number to add to the D20 roll when she demands a better price on magic items.

Bonus Action
One additional action on your turn.
This action can be taken either before or after your main action. Different Classes may have certain abilities/actions they can take for a bonus action. Spellcasters, such as Clerics –if we had one– could cast Healing Word as a bonus action and then attack with a weapon.
Talking to another party member is generally considered a free action, not a bonus. Not that Gozer would do that.
If the Bonus Action is used to cast a spell, another spell cannot be cast that turn, unless it is a Cantrip.

Disengage
Depending on your class, disengage is either a bonus action (Rogue) or a full action (everyone else). When you are in combat and engaged with the opposition and leave the 5 foot area around them, you provoke an Opportunity Attack. If you use your Action to Disengage before running away they no longer get that Attack.

Reaction
A Reaction is a special action that can happen on your turn or on someone else’s, and is once per round. An Opportunity Attack is a reaction.

Opportunity Attack
When hostile creatures are engaged with each other (within 5 feet and battling) but realize they no longer have “those feelings” and want to move away, the creature being left behind gets to perform one Opportunity Attack as a Reaction. This shows the other just how much their leaving hurts.

Hold Action/Ready Action/Delay Initiative
If your turn in Initiative order comes and you aren’t quite ready to act yet, you can delay and Ready your action. You can set a Trigger for when a specified action will happen before the end of the round. This uses your Reaction to do, and you only get one reaction per turn.

TPK
Total. Party. Kill. — It has been threatened.

PHB/DMG/DM-GM
Player’s Handbook. Dungeon Master’s Guide (or damage depending on context). Dungeon or Game Master

Melee vs Range
Melee means up close and personal attack – within 5 feet or yourself. Ax, hammer, swords
Range means greater than 5 feet away. Bows, javelins, magic

Finesse weapons
Lightweight weapons that use dexterity as its modifier. Rapiers, light swords

How Range weapons work
Range weapons all have numbers behind them: ##/###
A range of 5 foot up to the first number is the normal range of the weapon. The adventurer using it would roll one D20 as normal to attack. Between the first number and the second number the attack has disadvantage. The weapon CAN hit something in that distance, but it’s not as likely. The adventurer rolls 2 D20 and uses the LOWER number for their attack. Anything farther away that the second number is out of range and can not be hit at that time.

Spell Slots
Spells have levels from 0 (Cantrips) to 9. This is not the same as your adventurer level. Each Class has a different amount of Spell Slots per adventurer level per day. Low level spells can be cast in higher level spells slots, but not the other way around. Once a Spell Slot has been filled, it can not be used again until after a short or long rest.
Spells cast as a Ritual do not use a Slot.

Spell DC – Difficulty Check
When a target has to make a Saving throw against an attack spell, they must beat the Spell DC. That number equals 8+your spellcasting ability modifier+proficiency bonus (+any other special modifiers)

AC – Armor Class
The Armor Class in the number that has to be met or exceeded for a hit against the adventurer to strike them. Armor Class is based on dexterity — how fast you can move to get out of the way or block an attack. The base AC is 10+Dex modifier. Actual armor and a shield will add to this total. Barbarians are too awesome for that crap.

Initiative
Turn order in a fight. Each adventurer rolls their D20 and adds their dexterity modifier. The higher the total number, the faster that character acts/reacts to what is happening.

Saving Throw/ Skill Check
Roll a D20 and add your ability modifier for the specific type of Saving Throw. Different Class/Race/Back Stories give proficiency to specific Saves. Typically a Saving Throw is made when something is attacking you.
Skill Checks are made when you are attempting to do something. Class/Race/Back stories give you proficiencies in different skills.

Death Saves
Adventurers don’t usually die outright. Instead, when they get to 0 HP they are knocked unconscious, and are usually said to be bleeding out, because of the reason that made them go to 0 HP. Each time it is their turn in initiative order, instead of doing an Action they must now make a Death Saving Throw. 1-10 is a fail. 11-20 is a success. If they get 3 successes first, they are stabilized. If they get 3 fails first, however, they are dead. Dead dead.
Alternatively, if they have fellow party members that actually care about them, then one of them could perform a medicine check or use a medicine kit to stabilize and they no longer have to roll Death Saves.

Hit Dice
A “Hit Die” is the specific size of die used to determine how many hit points (or life) an adventurer has. A mighty barbarian uses a D12 as their hit die. Every level the PC either rolls their hit die once, adds their constitution modifier, and adds tat total tot heri current max hit points OR instead of rolling they can use the “average” for their hit die level. For the D12 that’s a 7.

Short Rest
When adventurers have been hurt, or in some cases used up spell slots, they party can agree to take a Short Rest. These last at least 1 fantasy hour and during this time the PCs can not do anything strenuous. They don’t have to sleep, but they can’t do aerobics either. If low on hit points, a PC can decide to roll Hit Dice to regain some. They will have 1 hit die per their adventurer level, which they will roll and add their CON modifier to each roll. Half of their expended hit dice can be recovered on a long rest.

Long Rest
A Long Rest is a longer version of a Short Rest, but with more benefits. A Long Rest must last at least 8 hours, again not necessarily sleeping, but not doing anything active. Long Rests usually take place overnight, with PCs taking turns keeping watch over their fellow party members. After a Long Rest, all Hit Points and Spells Slots are recovered, and some conditions are removed.

Temporary Hit Points
Some spells and special abilities give temporary hit points to an creature. For example, if you have 5 temporary hit points and take 7 damage, you lose the temporary hit points and then take 2 damage. And they don’t stack. So if a spell gives you 5 temporary hit points, and you cast the spell again to get 8 temporary hit points, you now have only 8 THP.