What are these UltraShorts? Are these some kind of stocks, bonds, derivatives, etc? Or are these just regular shorts made out of jeans?
Well, the Ultrashorts are sort of a fund that go in the opposite direction of the underlying Index. I will give a brief explanation below, however, you shoudl read ProShares site to get more details.
In short, the ProShares are ETFs that are designed to be traded like any stock using any brokerage. These are funds that go in the opposite direction of the underlying index. There are Short ProShares and then Ultra Short ProShares. Short ProShares are designed to go up when the index goes down and vice versa. Ultra Shorts are designed to give double yield. Hence, the Ultra part.
Examples:
Short Dow30SM
This will go against the DOW movement. So on down days, you buy this and expect it to go higher.
UltraShort Dow30SM
Others shorts/ultrashorts: QID (Nasdag 100 UltraShort), PSQ (Nasdag 100 Short).
So these shorts provide for a generic way to trade the market/index itself as opposed to trading a given stock which may or may not be trading along with your index.