Have no idea about a function model.apply

Beginners
1

I have seen some codes in others, but I have no idea about what it means

pretrained_model = BertModel.from_pretrained('bert-base-uncased')
 def add_no_init_flag(module):
        module.sz128__no_init_flag = True
pretrained_model.apply(add_no_init_flag)
  1. What is the meaning of apply
  2. What is the meaning of sz128__no_init_flag