What do we mean when we say it today?
Like we said before, you might run in to this phrase (or title of the song) at a high school graduation. If you think about it, that's pretty close to what Othello is saying about war, but with a modern twist. At a graduation, all the graduates dress up and march in a line together. There are awards, sashes, symbolic colors, and swelling of pride (and maybe even a few tears from mom and dad).
We think that comes close to the glory and ceremony of war that Othello's talking about here. Of course war is not all pomp and circumstance (in fact, most of it isn't), but that's what Othello is remembering about it, so that's what this phrase means.
The truth is, usually this phrase does have something to do with a grad ceremony or a formal occasion of some kind. It might just be us, but we don't run in to a lot of pomp and circumstance out on the streets.