load_state_dict(self.model, checkpoint['model_state_dict'])

This line of code loads the saved state dictionary of the model from a previously saved checkpoint into the current model. The `load_state_dict` function is used to load the saved state dictionary into the model, and the `checkpoint` variable is a dictionary that contains the saved state dictionary of the model.

The `self.model` is the current model object to which we want to load the saved state dictionary. The `checkpoint['model_state_dict']` refers to the saved state dictionary of the model, which is stored in the `checkpoint` variable.

Overall, this line of code is used in deep learning frameworks like PyTorch to resume training or inference from a previously saved checkpoint.