"Fabula" and "sujet" are terms from Literary Theory used to explain the difference between a story and its plot. "Fabula" is the chronological order of events, while "sujet" is the order events are told in (i.e. the Scene Sequencing). In most stories, these match up pretty closely, but this does not necessarily have to be the case.
They're from Russian Formalism, not French: it's pronounced "Sue Jet". Take, for example, the film Memento, where half the story is told Back to Front interspersed with segments told front to back. Or look at this graph of fabula vs. sujet in Memento. Complicated, huh? Postmodernists love this but the idea itself dates back to Aristotle.
If the fabula is very different from the sujet, the story is probably more about figuring out how the plot fits together than the plot itself, which can leave the plot, once figured out, kind of weak. This is part of why some people hate Time Travel stories.