"Plot is how the events in a story directly impact the main character."
Danger Will Robinson, danger. This way lies madness. Don't buy it.
Here's what Plot is:
Plot is conflict.
Plot is the problem that causes the character to change (positively or negatively).
Plot is the evolution of a premise (and premise is the thing that brought people to the story in the first place)
Here's what Plot isn't:
Plot IS NOT a series of impacts on a single character. (Plot has consequences far and wide, even if you're writing about a single character adrift in space)
Plot IS NOT the result of events happening (Plot is far too contiguous, interconnected and interdependent to just be a hodge-podge of "Oh by the way this happened")
Plot IS NOT passive. (Plot is a very active response to a changing (or possibly changing) environment)
What Plot boils down to is a choice in the face of a test.
Plot answers the question -- "When this problem (we'll call it X) occurs in a created world, how does the world respond, in ways large and small?"
To this thinking, plot could be on the small scale: the bully in the classroom or it could go large scale: the appearance of malevolent aliens coming to enslave mankind through smartphone apps....or something.
But there's a problem, and like the song says, yo, I'll solve it. The "I" in this case are the characters, not just the singular (or possibly titular) protagonist but the whole cast of characters - everyone from the sidekick to the doubters to the assistants to the random people who inject realism in flavor-text paragraphs.
Gamers, I'm looking at you here - Plot is why you've got people around your table. What are they doing? How will they respond? Why are they compelled to act in this way or that? How loosely or closely you play potentiality, that is to say how much leeway you give your players, directly ties to the strength of your plot and the potential of that plot.
If it's a closed loop, or you're working on a small scale, then the plot's pretty linear -- the party assembles and puts a righteous hurting on the badguy of the week. A wider view shows the problem isn't just held to one instance of a certain badguy, or that taking out this baddie reveals a power vacuum that other nasties will rush to fill. The point here is -- think of the plot's consequences, both good and bad, and then see if the plot needs tweaks. And try for narrative options, rather than narrative solutions -- the players should be the ones patching the holes, not the NPCs.
Writers, this one's for you -- The resolution of the plot WILL/CAN/SHOULD change characters, for better of worse. The problem might be one of internal struggle, or physical injury or whatever (I am loathe to name options here, lest I suggest there can only be certain kinds of plots).
Yes the above quote that started this rant has implications that suggest we're going to find out what the consequences of decisions are, but that's not the plot. The plot is a freight train that intersects all the paths of all the characters - the injuries and damage of collisions isn't the plot, that's the consequence of plot.
The plot IS the decision AND the reactions, not just the impact. The proverbial explosion had to get there somehow, and that's part of the story.
When in doubt, give the characters/players/actors/participants choice, and trust their decisions (which is made easier if you've given them a core philosophy) to let them show you how they're responding (yes, it's an active process) to the challenge of the plot.
Note: I feel like this post got away from me, I may revisit this idea later in the week.