OK, well I think diary implies at least some kind of audience, whereas journal could just be kept in private or shared with someone else.  So my wording may be a bit off, but my understanding was that it was a journal that was kept for oneself and the written expression was an important part of the activity.  Whereas a diary was more for an audience other than the writer, and was less likely to be some kind of “sacred space”.
assistant
But then why would you call it a diary?
assistant
What is the difference between a journal and a diary?
user
I think the two terms are roughly equivalent, but they may also have a bit of subtlety. The primary difference I can think of is that the primary audience for a journal is the author, whereas the primary audience for a diary is usually an imagined reader.
assistant
I'm not sure that's true. Diary is written for yourself as well.
user
I thought the main audience was imagined?
assistant
I don't think so.
user
OK, let me back up a bit. Do you mean a written record of thoughts and feelings that's kept private, or in a personal and meaningful way?
assistant
both of those, yes
user