What is a journal?

Interesting question:  this blog is a journal.  What's it for? 

To me, a journal needs:

• A writer, but not necessarily the writer.  That is to say that I can write as Janine, but I can also write my journal as Juliet for a literature class or as a 2 year-old baby for a psychology class or even as a tadpole for a science class.  "Dear Diary, today I sprouted feet..."
• A reason.  Am I using my journal to explore a question or to answer it?  Are my thoughts fully formed or are these half-baked opinions.  Do I expect to look back on this one day surprised at how little I knew, or am I recording an epiphany for all time?
• A reader.  Can I be the reader of my own journal?  Sure I can, but is that enough motivation to keep me writing everyday?  Maybe it might be better to have a reader, but not necessarily the reader.  So if I'm writing as Juliet, my classmate isn't reading my entry as my clasmate but as Romeo.  If my teacher is my reader, does my teacher have to be a teacher?  Or can she can just be reading my journal as a fellow traveller on the road to becoming a better teacher herself?

Have I answered my question?