Journal and diary

Diary of a Wimpy Kid:

First of all, let me say something straight, this is a journal, not a diary.

a record of what you have done, or of descriptions or thoughts, written each day or frequently over a long period.

journal

1 a serious magazine produced for professional people or those with a particular interest:
the British Medical Journal
2 a written record that you make of the things that happen to you each day [= diary]: He decided to keep a journal.

diary

1 a book in which you write down the things that happen to you each day [= journal]: Inge kept a diary (=wrote in a diary) during the war years.
diary entry (=what you have written for a particular day)
2 especially British English, a book with separate spaces for each day of the year, in which you write down the meetings, events etc that are planned for each day [= calendar American English]
Did you put the meeting date in your diary?