Welcome to the forum, but I'm afraid that your suggestion is not correct at all, @ForHere. They have apple does not mean that they have an unspecified number of apples. As Loob has explained, They have apple would suggest that they have a quantity of cooked apple, perhaps in the form of a mush or puree; it cannot refer to individual apples. In some contexts, it could also refer to flavour or type of something else. For example, if you ask what kind of juice people have, you could answer They have apple.At least based on usage, you can say They have apple (or I have apple: the pronoun is not an issue), and it would be correct for any number of apples that is one or more, shared or not shared.