Some hedge fund strategies are designed to make money when other assets are falling in value. Collectively these can be referred to as protection strategies. The simplest of these is a net short equity or credit fund but other types exit including Negative Correlation funds that seek out investments that benefit when certain asset prices fall.
Tail Hedging Funds are designed to benefit when extreme events occur. So-called Black Swan events (named after Australia’s Black Swans, an animal so alien to European minds that its existence couldn’t be foretold) could impact the value of all assets (when assets fall or rise in tandem they are said to be positively correlated). Tail Hedging Funds are supposed to protect against that risk. They do things like buying very out of the money derivatives (derivatives that won’t have any real value unless the value of the underlying changes significantly).