What I would consider the classic journal is much like a diary. It is a written or typed document with a series of dated entries that both records the writer’s experiences and their feelings about those events.
However, the difference between a diary and a journal depends on who you ask.
For some a diary and a journal are synonymous. They are both a daily record of what happened in your life. An article on the University of California, Berkley’s website by Kira M. Newman, titled “How Journaling Can Help You in Hard Times” uses the words diary and journal interchangeably. Newman emphasizes the writer discussing their feelings.
For others, including the Smithsonian Institute’s Archives of American Art, a diary and a journal are distinguished by the amount of reflection. The Smithsonian says that a journal is more reflective than a diary and focuses more on the writer’s feelings than on their activities.
Jeffrey Orrico of Sacred Heart University’s Library cites the Oxford English Dictionary as stating that a journal indicates “a more detailed account than that of a diary.”
Others say a journal is less private than a diary, noting the use of the term in classrooms, where the student expects a teacher to read what they write.
And still others, distinguish between a journal and a diary by the frequency of the entries, noting the expectation for a diary is daily and more varied for journals.
The variations of definitions listed above affirm what I have repeatedly said. Your journal is your journal. You decide what you are going to include and how often you make entries.
The only commonality that I think is generally expected is that you date each entry.