In the documentation, I find methods with arguments which seem unused. In the code examples, Any() with 1 argument Any<TSource>(IEnumerable<TSource>) is called with no arguments:

bool hasElements = numbers.Any();

and Any() with 2 arguments Any<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) is used with the second argument only:

bool unvaccinated = pets.Any(p => p.Age > 1 && p.Vaccinated == false)

What is the meaning of the first argument (here: IEnumerable<TSource>) in the documentation? I guess it is related to the object on which the method is called, but how does this syntax work?