A diary or journal is a book for writing discrete entries arranged by date reporting on what has happened over the course of a day or other period. Such logs play a role in many aspects of human civilization, including governmental, business ledgers, and military records.

Diaries by type and function

Diaries run the spectrum from business notations, to listings of weather and daily personal events, through to inner exploration of the human psyche, a place to express one's deepest self, or record one's thoughts and ideas.

Some use the words "diary" and "journal" interchangeably while others apply strict differences to journals, diaries and the practice of journaling (dated vs. undated, inner focused vs. outer focused, sporadic entries vs. regular entries, etc.). While traditionalist preferred the use of the term diary, the current preference (based on book and article titles) is to use the word "journal." The phrase "journaling" is often used to describe such hobby writing, similar to the term "scrapbooking."

 from : en.wikipedia.org