Imagine a shield shaped somewhat like an elongated kite or coffin with a bottom edge a foot wide or less. Those are usually what we call them, "kite shield" or "coffin shield." Instead of putting the straps on the back so your arm is across the shorter dimension, you put the straps so the arm goes down the longer dimension.
They're usually made of lighter materials, like corrugated plastic and camp/exersize mat, so they're extremely light. They move fast, and because what you've essentially done is made your non-sword arm longer, so you can sweep it down the body to actively block shots rather than just getting something in the way of a swing, like with a punch or traditional shield.
It often results in the bottom point of the shield being across your sword-arm shoulder, with your sword down below it, able to hit your opponent in the legs where they can't get a less mobile shield to block in time. It looks silly when someone squares up, until you realize that they can hit ankle-knee-hip-shoulder-shoulder-hip-knee-ankle around their opponent's body and if the opponent is unused to the style and hasn't learned to compensate, he or she has probably been killed by a rogue in a face to face fight in under 90 seconds.
The best thing about those shields is that they're ambidextrous, which has made lefties I know (who hate punch shields) light up like Christmas trees when they find one in an NPC camp.
