In World of Warcraft, what is a scenario? I see it has something to do with dungeons and raids but I don't know what it is. Please, can you specify?
A scenario is an instance that involves playable pieces of lore in Azeroth that are most of the time not involved with your character specifically. These "out of body" experiences contain stories of lore that is being played out in a non linear time-line. As you play them out, you are required to do various combat and non-combat events in order to move on within the story line of the Scenario. Like Raids and Dungeons, Scenarios have Mechanics and Heroic, which involve not blindly hitting every enemy that moves. Scenarios require either 1 person or can be done with a 3 person team with no role calls by default.
A scenario is like a mini-dungeon, but unlike regular dungeons, you aren't required to have a healer, dps and tank. You should be able to complete it with any combination of the three.
They usually involve certain events that you have to complete, like protect the village, or collect beer.
In WoD, a scenario called Proving Grounds is a single person scenario where you need to prove your skill in a certain role before being allowed to do heroics as that role. For instance, the healer proving grounds involved keeping a group of 4 other NPCs alive while waves of monsters spawn.