As someone who keeps both a journal and a diary I may be able to assist you with this (at least, from a U.S. American standpoint). A diary implies a book where one writes about personal thoughts, emotions, and/or secrets. This will usually be a much more private book that is not shared with people (or is only shared with a select few people). A journal tends to be more observational and factual. I keep a travel journal where I write down the things I have seen, done, or experienced in a particular place. I may talk about how a particular experience or place made me feel, but I won't write about with whom I am madly in love or about deep, emotional thoughts on the meaning of life. I would not be embarrassed or upset if my journal became public - in fact, I used to publish my travel journal online for the world to read! That being said, in British English a diary is normally a book where you write down appointments and events on particular dates. This is more commonly referred to as a "calendar" or "agenda" in North American English. I hope this has been helpful!