Welcome to Gaia! ::

Generally what that ACTUALLY is.. You'll generally see it more in actual cameras that use flash.. Basically

You have 2 shutters that go, the first shutter opens, revealing the image, letting in the light, and then the 2nd which closes...

Now what happens is with faster shutter speeds the 2nd shutter doesnt wait till the 1st shutter is done, the 2nd shutter is moving right behind the 1st shutter, so you have a little slit and the camera records each little line of the image as it moves horizontally across the image, so you have like short vertical lines across the image. With faster shutter speeds, the thinner the line generally is, longer shutter speeds, more of a gap... and the camera puts them all together and if there's a flash that goes off while its taking the picture, a part of the image, like a stripe like in your picture will be overexposed because that one slit, that one line where the camera was getting it saw the flash and so only that line is overexposed.

If this doesn't make more sense I can make like a whole tutorial with pictures that explains it all better.