Subversion is the quiet, hidden work of weakening something powerful from the inside — most often a government, but also a system, an institution, or a set of rules. The key feeling is secrecy and slow damage: not an open attack or a battle, but spreading ideas, passing information, placing people, turning others against the thing from within, until it no longer holds. This is why governments write it into their laws, and why the word turns up in spy stories, in political trials, and in charges brought against journalists and protesters.

Because it is a word governments use about their enemies, it is worth knowing that it is not neutral. Who counts as a subversive depends entirely on who is speaking. The same action can be called subversion by one side and honest opposition by the other. Taiwanese students will recognise how heavily the word has been used in the region's political history.

There is a second, much lighter use that is now very common in talking about art, film, books and games: the subversion of a rule or an expectation, meaning that a work sets up something familiar and then deliberately breaks it — "a clever subversion of the fairy-tale ending." Here the word is a compliment. Same idea underneath, undermining from within, but no danger and no crime.

It is usually uncountable in the political sense (accused of subversion) and countable in the artistic one (a neat subversion of the genre).