About the difference between the term "generalization error" and "test error" in the deeponet paper

[BraveDrXuTF]

Dear Dr Lu,
Hello, I want to ask a question about the difference between the term "generalization error" and "test error" in the deeponet paper.
Here, you wrote 'the error of a neural network for previously unseen data', so I understood it as same as 'test error',

also, in some of the web results 1 2 seem also approve that: generalization error and test error are the same thing.

However, in fig. 3 abcd you gave subfigures with the test error and generalization error independently, that's why?

[Lu Lu]

Here generalization error = test error - training error.

[BraveDrXuTF]

Thanks. I get it now.