I believe a diary is where you write daily about what you did & a journal is where you write whenever you feel like it. Journals can contains poems, drawingings, etc. Whatever it takes for you to get your feelings out on paper.
It doesn't really matter that much though. The thing that matters the most is whether or not you get what you're feeling out. In a journal (or a diary) you can write whatever you are thinking/feeling with worring about what others will think or if it will hurt someone else's feeling since both are for your eyes only unless you choose to show someone else.