So, what makes an art journal? A journal is defined as:
A daily record of news and events of a personal nature; a diary.
And art is defined as:
The expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power.
So one possible definition, if you want to be kind of technical about it, is, "Art Journaling is the expression or application of human creative skill and imagination to produce beauty and express emotional power in the daily recording of news and events of a personal nature."
I think of art journaling as expressing what ever the &^%$ is going on inside in some creative and ascetically pleasing way. It's to me and for me. It's all about me, me, me, me, me. No apologies for that either. And I am not trying to win any art shows, impress my friends or even have it make sense. And I can honestly tell you I don't think I have any single page that I consider finished. Everything is open to updating, painting over and bring ripped up to be used in another page. I also don't have any pages yet that I feel are "good" ascetically; but the ones that are close, they make me feel all warm and tingly. So that is part of my definition. A creative expression of what ever is going on inside me that when I look at it makes me feel like a bell has been rung deep inside me.
The picture at the top is of a page I love. No words, except what is buried under paint. No design, and no intention of anything other than a happy mess on top of tokens of my life. I look at it and see all sorts of things no one else is ever going to understand.
Daisy Yellow has a really nice post about it too.