This is something that I've been pondering. I say, "I have $number of books" on my ereader and "I have $number more saved on my computer" but what I really mean is I have that number of files which are on or available to be sideloaded to my ereader. That does include the magazine article on HP fanfic that I still haven't read. That includes the stories from AO3 that are 8,000 words. (I rarely download from AO3 if stories are 6k words or less. Those, I just read on my laptop screen.) It includes a free short stories that I've downloaded for free from elsewhere - although I tend to not read original short stories unless they are part of a larger universe that I'm already reading in. That includes a few tech manuals and a privacy policy/ToS from a website that I'm thinking of using but need to read before I'm willing to commit any personal data to the site for sharing or storage. So what I really should say is, "I have $number of ebooks on my ereader and $number of other files which aren't books as well." However, I'm rarely precise. If I start thinking about it too hard, I just say, "I have about $number of ebooks" and let that be that.