Triple dot notation python

Question

I looked through some python modules, in the builtins.pyi i found some method definition using ... what does this mean? Im aware the others are annotations of the methods.

class set(MutableSet[_T], Generic[_T]):
    def __init__(self, __iterable: Iterable[_T] = ...) -> None: ...
    def add(self, __element: _T) -> None: ...
    def copy(self) -> set[_T]: ...
    def difference(self, *s: Iterable[Any]) -> set[_T]: ...
    def difference_update(self, *s: Iterable[Any]) -> None: ...
    def discard(self, __element: _T) -> None: ...
    def intersection(self, *s: Iterable[Any]) -> set[_T]: ...
    def intersection_update(self, *s: Iterable[Any]) -> None: ...
    def isdisjoint(self, __s: Iterable[Any]) -> bool: ...
    def issubset(self, __s: Iterable[Any]) -> bool: ...
    def issuperset(self, __s: Iterable[Any]) -> bool: ...
    def remove(self, __element: _T) -> None: ...
    def symmetric_difference(self, __s: Iterable[_T]) -> set[_T]: ...
    def symmetric_difference_update(self, __s: Iterable[_T]) -> None: ...
    def union(self, *s: Iterable[_S]) -> set[_T | _S]: ...
    def update(self, *s: Iterable[_T]) -> None: ...
    def __len__(self) -> int: ...
    def __contains__(self, __o: object) -> bool: ...
    def __iter__(self) -> Iterator[_T]: ...
    def __and__(self, __s: AbstractSet[object]) -> set[_T]: ...
    def __iand__(self: Self, __s: AbstractSet[object]) -> Self: ...
    def __or__(self, __s: AbstractSet[_S]) -> set[_T | _S]: ...
    def __ior__(self: Self, __s: AbstractSet[_T]) -> Self: ...  # type: ignore[override,misc]
    def __sub__(self, __s: AbstractSet[_T | None]) -> set[_T]: ...
    def __isub__(self: Self, __s: AbstractSet[object]) -> Self: ...
    def __xor__(self, __s: AbstractSet[_S]) -> set[_T | _S]: ...
    def __ixor__(self: Self, __s: AbstractSet[_T]) -> Self: ...  # type: ignore[override,misc]
    def __le__(self, __s: AbstractSet[object]) -> bool: ...
    def __lt__(self, __s: AbstractSet[object]) -> bool: ...
    def __ge__(self, __s: AbstractSet[object]) -> bool: ...
    def __gt__(self, __s: AbstractSet[object]) -> bool: ...
    __hash__: ClassVar[None]  # type: ignore[assignment]
    if sys.version_info >= (3, 9):
        def __class_getitem__(cls, __item: Any) -> GenericAlias: ...