Restaking lets the same stake back more than one system. The validator agrees to extra rules imposed by the services they secure, and in exchange earns additional fees on top of base staking rewards.
The stacking of conditions is the risk. One stake now faces several independent ways to be penalised, and a fault in any secured service can cut the same capital. Correlated failures across services sharing operators are the scenario researchers worry about, and the models are young and untested at scale.
Layers compound the opacity: liquid restaking tokens sit on top of liquid-staking tokens on top of staked assets, and a discount at any layer propagates to the ones above. Advertised yields rarely show the slashing exposure being taken to earn them.
Related: liquid-staking, slashing, staking, yield-farming