>>717812881It's a gradating scale that depends on how closely you stick to known physical laws, typically called 'hard' or 'soft' scifi for its proximity to science fantasy.
Scifi typically has a couple central macguffins that do whatever reality altering bullshit that changes the setting to what the author wants to explore (for example, FTL drives) and then everything else behaves as if its normal and real. Maintaining this feeling of 'this could be real' is called verisimilitude.
Take mass effect for example:
>element zero reverses electrons or w/e it was>this lets you cast magic spells and makes antigravity realeverything in the setting that's unreal/impossible now stems out of this
the suspension of disbelief for the setting is ruined when things start to happen that don't follow the rules set beforehand, like having the new Volvo show up in your D&D session suddenly. Yeah, the setting is magic and fantasy (or scifi) but within that setting is an expected reality and when you shatter that you break the versimilitude.
A LOT of settings, stories, and modern franchises especially, break the fuck out of the established lore and world building because some hack retards don't know how to write fuck about shit.