Something just happened. Did it work? How much? Fast enough? Where is everyone involved, now? Are you hurt? Tired?
No matter what system you're using, stuff happens in play. When that stuff involves doing something, then someone eventually describes it and says how it turns out. That's narration.
Don't mix it up with the ordinary idea of talking, which is going on all the time. I'm talking about when actions are taken, and we want to know how they turn out. When someone describes it (with or without any various mechanics being involved), that's narration.
Also, some games are really vague about who gets to do this, relative to somebody carrying out a resolution mechanic, and some are really specific. Knowing how narration relates to IIEE is a big part of understanding a game's Resolution methods. Obviously it's tied directly to Effect (the last "E"), but Effect is not always procedurally separate from the other things depending on the game.
See also Authority because Narration Authority is one of the four types.
A type of Ephemera. What is said by a game participant to alter or add to the Shared Imaginary Space (sic -ll) during Resolution, especially Effect. How narration is distributed among participants varies widely, see Authority; to be fully accepted, narration requires Credibility. Central to but not limited to Drama Resolution.