In
Greek drama, violent or unsavoury acts tended to happen off-stage, or 'off-scene', which is where the modern word 'obscene' comes from (more precisely, '
ob' is Latin for 'against', whilst 'skini' is Greek for 'scene', or 'stage'. 'Obskini' has become 'obscene' in the intervening centuries).
Technically it refers to any dramatic element which we do not see with our own eyes, and which we are merely informed about. In 'Star Wars: A New Hope', for example, the Imperial reconnaissance of Dantooine is 'obscene'.
Nowadays the word is generally used to refer to something with lascivious content, although it can often refer to something which the commentator believes should be kept hidden (as in the phrase 'Omni Consumer Products announced that CEO Dick Jones earned an obscene $12 million in bonuses alone during the last financial year, despite widespread industrial action, anarchy in the streets, and unconfirmed reports of metal policemen gunning down civilians at random during humid weather').