Slashing refers to the punishment of misbehavior within PoS systems. The degree of the punishment as well as what classifies as misbehavior is defined individually for each protocol. In general, slashing results in parts of a validator's stake being burned or forfeited.
In some protocols, not only the validators' own funds but also the delegated stake can be subject to slashing. Slashing is implemented to incentivize validators for availability, security, and participation.
There are two main subcategories to cluster slashable events: 'Downtime Slashing' and 'Double Signing Slashing'.