Definition of Science Fiction
Darko Suvin, in his Metamorphoses of Science Fiction, defines science fiction as “the genre of cognitive estrangement” (Metamorphoses 4). Cognitive is defined as:of, relating to, being, or involving conscious intellectual activity (as thinking, reasoning, or remembering) 		based on or capable of being reduced to empirical factual knowledge
(Merriam-Webster)Estrangement is defined as:to turn away in feeling or affection; make unfriendly or hostile; alienate the affections ofto remove to or keep at a distanceto divert from the original possessor
(dictionary.com)

So cognitive refers to things that we know empirically or observe. Estrangement is a separation from something. Pairing these, we get a separation from what we understand to be factual (science) and what we—or, in the case of literature, our characters—do (fiction), which is where Suvin bases his definition of science fiction.

Given this definition, Suvin’s idea of science fiction might seem to be along the lines of fantasy, something that goes against our understanding of the natural world. However, he addresses this, saying that fantasy is not an inconsistency between our current knowledge and what happens, but a disregard for our current knowledge with regards to the events of the story (Metamorphoses 7-8). Science fiction, on the other hand, is aware of this knowledge and approaches it in ways that are different from our current understanding.

This definition is very similar to how Robert Heinlein and Asimov regard science fiction (Turning Points 10, 33). In his essay “Social Science Fiction,” Asimov discusses the idea of science fiction as extrapolation based upon what we know, resulting in imagining “fictitious societies as possessing potential reality rather than as being nothing more than let’s-pretend object lessons” (Turning Points p. 33). Heinlein compares this extrapolation to “a man [looking] out a train window, [seeing] that another train is coming head-on toward his own on the same track—and [predicting] a train wreck” (Turning Points p. 12). All three ideas state that a story must acknowledge the existence of science, but take certain liberties with the current knowledge, though none that are, at least at the time, truly impossible.