A "hook" is a function that can be registered on a Module or a Tensor. It will be called when a forward or a backward call is executed on a Module or when a gradient is calculated with regards to a Tensor. In the case of a forward hook, it will be passed the module it is registered on and the input and the output of the operation.

• Module#register_forward_hook
• Module#register_backward_hook
• Module#register_forward_pre_hook
• Tensor#register_hook