What is an Encounter? (DMG)

An encounter is best defined by two broad criteria. If the described event lacks either of these, it isn't a true encounter. It may be a described scene, an event, or a bit of mundane business, but it is not a role-playing encounter.
First, an encounter must involve a thing, an event, NPCs (characters or monsters), or a DM-controlled player character. A meeting of two player characters (handled by the player alone) is not an encounter. It is an action between the players themselves.
Second, an encounter must present the possibility of a meaningful change in a player character's abilities, possessions, or knowledge, depending upon the player's decisions. The keys here are meaningful change and player decision. For each character with 500 gp in his pocket, going into a tavern and spending three gp on drinks is not meaningful change. If the character had to spend the same 500 gp in the same tavern to get information about the Black Tower across the river, the character has experienced a meaningful change-he's now broke.
If the player doesn't make a decision, then he's just coasting along, letting the DM do everything. Going to the tavern and spending three gold pieces on food and drink isn't much of a decision. Choosing to go bankrupt to learn what may or may not be useful information is fairly significant. The player is going to have to think about the choice. How badly does he want this information? How reliable is this informant? Does he need the money for something else-like new equipment? Can he get a better price?
The presence of an active force and the possibility for change based on player decision are what make a true role-playing encounter. Take, for example, the situations given below. Try to figure out which of the four is a true encounter, as defined above.
# Rupert and Algorond, a gnome, are exploring a cave. Algorond is in the lead. Without any warning the ceiling directly over him collapses, crushing the little gnome instantly. He is dead, and all Rupert can do is dig out the body.
# Rupert, a 10th-level fighter, meets three lowly orcs. They charge and, not surprisingly Rupert slices them to ribbons. He isn't even harmed. Searching the chamber, he finds a sword +1. Rupert already has a sword +3 and is not particularly interested in this weapon.
# Rupert reaches into his pocket only to discover that the gem he pried from a heathen idol is gone! Thinking about it, he decides the only person who could have taken it was his fellow party member (and player character) Rangnar the Thief. Unhesitatingly, he whips out his sword and holds it at Rangnar's throat. Rangnar reaches for his hidden dagger.
# Rupert and Taras Bloodheart are riding across the plain. Just as they crest a low ridge, they see a cloud of smoke and dust in the distance. They halt and watch for a little while. The dust cloud slowly moves on their direction, while the smoke dwindles. Moving their horses to a hollow, the watch the approach of the mysterious cloud from a thicket.
So, which of these four is a true encounter? Only the last one. The first didn't involve any player choice. The gnome is crushed, and there wasn't anything either player character could do about it. Not only is this not an encounter, it isn't fair. It could have been an encounter (with a trapped ceiling), if there had been signs beforehand (clattering stones, previous deadfalls, groaning stones) and if the gnome had been given the opportunity to act before the rock squashed him. The player choice could have been to heed or ignore the warnings and leap forward, back, or stand confused when the rock fell.
The second had player choice, but it wasn't particularly meaningful or balanced. The player knew his character could win the combat so his choice to fight was insignificant. He knew the sword was less potent than the one he already had, so his choice not to keep it was, likewise, not a choice at all. The situation could have been an encounter if the orcs had actually been ogres concealed by an illusion or if the sword had special unrevealed powers. Either of these would have made the character's actions meaningful.
The third situation has all the trappings of an encounter. There is meaningful choice and anything could happen next. However, this is a squabble between player characters, not something the DM has control over. It does not further the plot or develop campaign background. Indeed, such disharmony will only hurt the game in the long run. It could have become an encounter if an invisible NPC thief had done the deed instead of Ragnar. Rupert and Ragnar, eventually realizing the confusion, would have suddenly found themselves united in a new purpose葉o find the culprit. Of course, there would also be role-playing opportunity as Rupert tried to make amends while Ragnar remembered the insult!
The fourth example is a true encounter, even though it doesn't seem like much is happening. The players have made significant decisions, particularly to stay and investigate, and they are faced by an unknown creature. They do not know what they face and they do not know if it will be for good or ill. The dust cloud could be a djinni or a hostile air elemental. It could be a war-band of 100 orcs or giant lizards. The players don't know but have decided to take the risk of finding out.
In role-playing games, encounters fall into one of two general categories: planned (or placed) encounters and random (or wandering) encounters. Each contributes to the overall excitement and adventure of the game.