Many writers are described as Magic Realists when in fact they aren't. Magic Realism doesn't really have a specific mandate and yet ther are some rules; and while it is good and healthy and wise not to apply overly strict criteria in one's own fictional use of it, before breaking the rules it's also good to know what the rules are. Magic Realism isn't just a hazy definition but a precise term for a precise thing (Terry Pratchett defined Magic Realism as "fantasy written by someone who has gone to university"; he was wrong).
It's the same with Surrealism and Absurdism. They don't just mean what you want them to mean or think they might mean (i.e. stuff that's a bit weird or doesn't make sense). They have specific manifestos: Surrealism is intimately connected with Freudian psychoanalysis; Absurdism is intimately connected with Existential philosophy, etc.
It's fine to take elements from those movements you agree with and discard the rest, and it's even possible to argue that the original meanings have changed over time and that the correct definitions are now those of modern consensus, but again, it's nice to learn the original meanings too, just to give yourself a firm basis to show what you're working from.
One of the problems with lazy definitions of Magic Realism in particular is that misunderstandings of its intentions and techniques can produce embarrassing work. John Updike, for example, was so enamoured of the surface effects of such writers as Gabriel García Márquez and Jorge Amado that he wrote a novel (called Brazil) full of the effects without the rationale. In true Magic Realism people don't just start flying for no reason whatsoever or because it's pretty: the flight is a concrete symbol of an emotional state (intense happiness, for example).
Magic Realism simply means a style of fiction where the author doesn't write about how the world actually is, but how it sometimes feels... So it's emotionally based, rather than intellectually, politically or philosophically based. It uses exaggeration, overstatement and grandiosity to put over a wholly subjective world view (inter-subjective world view really, because all the different subjectivities should interact and modify each other). Understatement has little or no place in Magic Realism.
There's a character in One Hundred Years of Solitude who has bad wind. In Realism it would simply be stated that he farted loudly; in Magic Realism his farts kill sparrows in mid air and wither palm trees. This doesn't mean (as Updike seemed to think) that the sparrows really were killed by the fart, but that the fart was so powerful it felt like a phenomenon that might kill sparrows in mid air. So Magic Realism makes very heavy use of symbolism. Every significant event is a symbol or extended metaphor.
And yet, even though all the events are determined by a literal application of feeling, those fantastical events are presented in a very deadpan style. So if someone is deliriously happy they might start flying, but nobody around them will comment on this, or even note it, because the flying is actually internal.
I now expect to told that actually Magic Realism has always been an ambiguous term. Yes, that's true, but the above is a good place to start for a definition.
