Most text editors call it "file" or "document," even if it's not yet backed by disk.
It's a subtle difference, but I think emacs's decision to call them "buffers" (though it makes the editor a space-alien by modern standards, that much harder to learn) makes more clear that the user should have no expectation that any of the buffers ever get backed to long-term storage. Once one wraps one's head around that, a lot of things get much easier (including and especially writing document editing functions; where most systems would have you store blobs of text in string variables, emacs really wants you to pop up temporary buffers and manipulate them like any other buffer, with the added benefit that if a function fails mid-execution, the regular buffer editing tools make it easy to inspect the failed state).
It's a subtle difference, but I think emacs's decision to call them "buffers" (though it makes the editor a space-alien by modern standards, that much harder to learn) makes more clear that the user should have no expectation that any of the buffers ever get backed to long-term storage. Once one wraps one's head around that, a lot of things get much easier (including and especially writing document editing functions; where most systems would have you store blobs of text in string variables, emacs really wants you to pop up temporary buffers and manipulate them like any other buffer, with the added benefit that if a function fails mid-execution, the regular buffer editing tools make it easy to inspect the failed state).