[Python] When is a function in a standard library module called a built-in function?

I am confused about the term "built-in" function. I thought it meant only those functions built into the interpreter and documented in - 2. Built-in Functions
But it appears that functions defined in standard library modules are also built-in functions (in some cases). For example -

>>> import os
>>> os.chdir
<built-in function chdir>
>>> import warnings
>>> warnings.warn
<built-in function warn>
>>> import json
>>> json.dumps
<function dumps at 0x7f3643a240d0> # not built-in
>>> dir
<built-in function dir>
>>>


So when is a function in a standard library module called a built-in function and when is it not?

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