Sentence:  It seems that this ‘point of difference', the thing or things that differentiate the world portrayed in science fiction from the world we recognise around us, is the crucial separator between SF and other forms of imaginative or fantastic literature. The critic Darko Suvin has usefully coined the term ‘<WSD>novum</WSD>', the Latin for ‘new' or ‘new thing', to refer to this ‘point of difference' (the plural is ‘<WSD>nova</WSD>'). An SF text may be based on one <WSD>novum</WSD>, such as [...]. More usually it will be predicated on a number of interrelated <WSD>nova</WSD>, such as [...]. This ‘<WSD>novum</WSD>' must not be supernatural but need not necessarily be a piece of technology. 
Meaning of the word marked with <WSD> tags:  An innovation which is fictional, but, following the logic of cognitive estrangement (characteristic of science fiction), is lent plausibility by the assumption that the fictional universe is scientifically consistent.