As Bandit originally asked this: “Others use it and I’d like to understand from their point of view what it is and how it is unique.” I’ll give my 2p even though Rich pretty much nailed it with his first sentence.
From my POV it is simply a game – or series of games – that goes beyond the usual 1.5k pointer bashes and involve a growing storyline where characters – be they individuals, generals, units, ships etc. – work their way through a campaign, war or event.
I don’t think you need any specific mechanism for this but you do need players with the imagination to carry it through. Hence it will be unique because people are. For ex, I took part in an ECW campaign where we all indulged in silly names and back stories for the commanders. Only one relented because he ‘didn’t approve of silly names’. He likewise could not understand the incident where one officer charged into a formed pike block alone rather than be taken prisoner. It wasn’t in his make up to follow the narrative where the opposing commander had morphed into a Jacobean version of Uncle Monty from Withnail and I, complete with wagon-mounted man-cage…. We had no rules for this, it didn’t need any. It just developed from banter. The chap who didn’t get it was a competition player and it just wasn’t his thing.
All my fondly-remembered games have involved a narrative of some kind. Without it games just seem that much colder.
More nonsense on my blog: http://battle77.blogspot.com/