The missing man formation is just what it sounds like; a formation of aircraft with a slot empty. It's done to commemorate a fallen pilot, but also is often used when a national leader or such dies.
It can be done in a few ways. The slot can be left empty or, more spectacularly, the 'missing' aircraft can peel off to leave the slot empty. More spectacular still, though, is the variant wherein the aircraft leaving the formation climbs straight up to leave the empty slot. I've seen it and no video, unfortunately, can really convey the impact of that sudden climb. Not only is it a breathtaking manoeuvre, but the symbolism brings your heart into your throat.
[EDIT: I'm not sure of the reliability of this, but it's interesting enough to mention. Apparently, by tradition, the aircraft leaving the formation always heads west afterwards. This is just supposition on my part, but I'd be willing to lay a small wager on that tradition having originated in the WW1 pilots' expression, 'gone west', meaning that a pilot had been killed in action. The next part I have on slightly better authority; I happen to remember that W E Johns, in the glossary of one of the early Biggles books, explains that as a darkly humorous play on Horace Greeley's 'go west young man'.]
Anyway, that's the explanation out of the way. What prompted me to post this video was nothing to do with all that, really. Rather, it was the amazing juxtaposition involved. This was a flypast in honour of Prince Bernhard of the Netherlands, who died in 2004 (yes I know I'm late; I just ran across it on YouTube), by a flight of F16s with the missing man position being taken by a venerable old bird which will quicken the heart of anyone with any interest in the history of manned flight; a Spitfire. Indeed, according to a programme I watched recently, it still tops polls of 'favourite aircraft' in Britain to this day. And catch the rate of climb when it leaves the formation. Sixty years or more old but still no slouch, by any standard. R J Mitchell would have been proud! Anyway, I thought the video was worth sharing with anyone else who grew up with permanent patches of Airfix glue on the pads of their thumbs…
(Trivia fact of the day: When Prince Bernhard was cleared by British intelligence during world war 2 (he was German by birth), the person who screened him was none other than Ian Fleming.)