"Something happening" is not always a plot. Even in fiction, it may be nothing more than incident.Rechan said:The PCs stumble across a cult who are doing something. THAT IS A PLOT. Something is happening.
"Plot," according to Samuel L. Delaney, is "an illusion the writer ought to disabuse her- or himself of pretty quickly, too, at least if she or he ever wants to write anything of substance, ambition or literary richness. ... What there is, is narrative structure." Pick up a Delaney novel to see his theory in practice. Pick up a Thomas Disch novel for further disjunction.
One thing such thoroughly modern fictions have in common with the old "well crafted tale" is that they have been written down. What is to happen is what always happens. That narrative structure -- in the generic sense, as there are many specific structures -- is what we tend to be talking about here when we speak of 'plot' in a game.
Even more particularly, we are speaking of the program presented to players in what these days are commonly called 'adventures', the sequence of scenes leading to "the climactic showdown with the BBEG" and so on.
A hint: the article 'the' in place of 'a'.
A sequence of scenes that is just one of many possibilities, no more or less 'appropriate' than any other that does or does not lead to a person who may or may not be an enemy (may even be an ally) depending on how, if at all, the players choose to engage him or her ... that is not a plot.
"The Starship Enterprise encounters an alien with godlike powers" is not a plot. It's a premise (and also a cliché). Fill in the blanks that it seems to be _______, but is really _________ and trying to ___________ -- and that is still not a plot, except in the sense of what the godlike alien is 'plotting' (which is not the same thing).
If the alien with godlike powers is an author -- or game master -- forcing the character-players into conformity with a narrative structure, then that is a plot in the sense we mean.