My thoughts on this is that the Suspension of Disbelief is what we have to take for granted in order for the story to play out.
Therefore, it stands to reason that all stories have something that you need to suspend your disbelief in order for the story to work.
Some require you to just accept a small change (historical fiction or westerns), some require you to accept more fantastical things (science fiction/fantasy), but all stories have a suspension of disbelief by nature.
For example, in a fantasy setting, we assume that dragons, magic, and other fantastical things exist, because they need to in order for the story to work.
For science fiction, we assume that extra-terrestrial beings exist, and are intelligent, forming complicated civilizations, and that faster than light travel exists, otherwise, the story wouldn't work.
HOWEVER
People are more willing to accept something that couldn't happen in reality if it is justified. For example, magic doesn't exist, but for a fantasy story, if the author or writer can describe a system of magic that makes sense in the context of the story's canon and such, then people are more willing to accept that magic exists.
Now, any object traveling faster than light would be impossible, because according to Einstein, the object would have to expend more than an infinite amount of energy to travel faster than light.
HOWEVER
People are willing to accept faster than light travel if the writer gives a clear way of how the travel works, like, for example, you can travel great distances by folding space and time to create a wormhole, or something like that.
Mass Effect's Mass Relays are a great example, as is Halo's Slipspace Jumps, all are explaining FTL travel, so that the story makes sense.
Notice the thread here.
IT HAS TO MAKE SENSE.
Stories aren't an accurate descriptor of real life and all of its randomness. They're constructs. Thus, a story has to be written where it has a clear beginning, middle, and end with conflict threading all throughout the story.
Stories, by definition are characters, settings, and plot, all connected by conflict or drama, and filtered by how the story is told.
Thus, I can accept magic being a thing in a story, but I won't accept a character acting in a way that doesn't make sense, or go against who they are.
For example, I accept that Homer Simpson is stupid, and it's necessary for some of the gags in the Simpsons, but if Homer all of a sudden starts acting responsible, reasonable, and intelligent, and no explanation is given, then it's breaking my suspension of disbelief.
So as long as something makes sense, the willing suspension of disbelief remains intact, but if something breaks that, or creates a hole in it, and no sufficient justification is given, then the willing suspension of disbelief is broken, creating a plot hole.
Anything that takes you out of the narrative and has you go, "Wait a minute, that doesn't make sense," is what I would consider breaking that suspension.