Long/Short Equity

See: Long/Short Fund. Then note that here, equity is specifically called out as the long/short security vehicle. But then bonds feel sad and left out. They too can be longed and shorted; they're just not nearly as liquid as equities, so when hedge fund people want to deal with long/short bond-y stuff, they usually focus on currencies/macro things and global credit swaps instead of, say, individual series of corporate bonds, which are usually massively less liquid.