ARB stands for "arbitrage," and refers to a difference between the price of a security and the known value. For example, there are some blockbuster warrants that will cash out, or "delist" (i.e., be removed from listing on the Exchange) at H$0, because they did not make their strike price. The strike price for Angels and Demons is H$150. If it makes more than $150 million in domestic box office by Labor Day, the Blockbuster Warrant will cash out at the difference between the final total and $150 million. But Angels and Demons has only made $133 million so far, and there is no way it can make $17 million in the next week. So we know that that Blockbuster Warrant, BWAND, will cash out at zero. But the price of the warrant cannot be zero, it has to be at least one cent. Which is what it is (the minimum used to be six cents, so this was more lucrative before version 4 of HSX). So if you short that Blockbuster Warrant, you are guaranteed to make one cent per share. 10,000 shares will cost you $100, and you are guaranteed to make money. If you do it during the commission-free period, you won't pay any commission at all, since you won't pay any commission on the delist, either. There are several blockbuster warrants like that. Indie films nearing the end of their run tend to be excellent arbitrage opportunities, too.