character: like a character in a play, a person/creature who exists within the plot of the game or story.
player: the person (actor) who pretends to be the character, and makes the decisions and performs the actions that the character would make.
non-player character (NPC): a character who exists in a game, but who is played by the GM (in a TTRPG) or people who are not players within the game (in a LARP). NPCs are often but not always opponents, monsters, etc.
LARP (Live-Action RolePlaying Game): a game in which players physically play their characters, much like the actors in an improvisational play. Every action the character takes (including combat) is represented by an action (usually either a physical action or a verbal keyword or short phrase) performed by the player.
TTRPG (TableTop RolePlaying Game): a game in which characters do not physically exist, but are represented on paper by descriptions, traits, abilities, etc. As with all roleplaying games, the player decides every action that their character performs, and communicates it verbally to the gamemaster (GM), who determines the outcome.
gamemaster (GM): the person running the game. The GM creates the setting (story), describes what the characters see, what happens to them, the actions of NPCs, etc., and arbitrates as needed. Sometimes also called a marshall (in LARPs) or a dungeonmaster (DM).
marshall: see gamemaster (GM)
dungeonmaster (DM): see gamemaster (GM)
die (plural: dice): a polyhedron with numbers on each face, used to randomly determine an outcome. Dice are usually described by the number of faces. For example, a d6 is a 6-sided die.
stat (statistic): how good a character is at a particular ability or class of abilities. Usually described as a number.
health: how physically healthy a character is. (Often described by a number of “hit points”.) A character who is wounded has lower health until healed, either by a character with medical ability or magical healing ability.
mana: magical potency. (Often described by a number of “spell points”.) This determines the number and strength (potency) of spells that a character can cast. Mana is usually recovered by a “long rest” (e.g., overnight while asleep).
hit points: see health
spell points: see mana
fall radius: a distance away from a player that is equal to the player's own height.